• #Timeline Plan

  • Introduction

    Literature

    History of C Seq
    Different ways to model
    Impact of myc fungi
    Carbon Coalition & small-scale data

    My research

    Sheep unit pastures
    Intensive rotational grazing
  • Materials & Methods

    Soil sample collection

    How we randomized it
    Bulk density collections
    Different depths & labels
    Air-dried, homogenized, sifted through 2mm sieve
    CN machine

  • Results

    Statistical analysis

    Bulk density
    Mass of C in pastures
    Mini tab
    Two-factor ANOVA
    95% confidence interval
    Power analysis

    Tables/Figures

    Soil survey map of pastures
    Samples and CI
    Power analysis?
    Raw data
    Equation for finding mass of carbon

    Statistical analysis

    What we have found: in five years, we are confident that we will be able to monitor a change in carbon
    However: what is the change from?
    Plan to change management practices

  • Discussion

    Direct vs indirect methods of sampling

    How many samples are needed

    Spatiotemporal variability and randomized sampling

    We don’t know how management cahnges SOC but we will be able to tell if it changed

    Importnat to find a practical methology for future establishments in carbon markets

  • Conclusion

    What this research means

    Compared to literature
    Soil Carbon Coalition

    Call for further research

    Need to do this study on a larger scale
    Encourage producers to establish their own baesline data
    Preparation for a carbon market?

  • Literature Cited

  • Climate change

    Broad climate change statement
    What is carbon seqestration and how does it fit into the picture
    Specifically: grasslands and carbon sequestration (statistics, etc.)

  • Biomechanics of carbon sequestration

    Natural vs anthropogenic
    3 ways of natural seq: litter decomposition, root decomposition, root exudates
    Longevity and protecting it from decomposition

  • Variability and controversy

    Models that are telling us to sequester very little
    Spatiotemporal variability in topsoil

  • The untold role of mycorrhizae

    Christine Jone’s “liquid carbon pathway”
    What myc fungi does
    Why we haven’t put it in the equation
    Why it means modeling might be wrong
    What’s the only way to tell? More sampling on smaller scales

  • Sampling

    We took soil samples from two pastures that represented the high and low quality spectrum of the ranch. Pasture 1 had been grazed periodically for several decades, had been irrigated since [ ] ?? and had limited traffic across of it. Pasture 2 had been eliminated from the grazing plan, but had been grazed periodically as needs changed. Pasture 2 was adjacent to the barn facility, and had an old silage cement bunker and a carport on it, so there has been considerably heavier vehicle traffic across the pasture.
    Biological monitoring

    The transects were chosen in a part of the pasture that seemed qualitatively representative of the entire pasture. Transect tape was laid down for 200m, and the center of the testing site was chosen at 50m. The transect was marked with physical guidelines (i.e. positions of utility poles, fence posts, and other physical characteristics that were not likely to change), compass bearing, and latitude/longitude bearings. The transect was divided into a 10m plot with sampling sites every 1 sq m.

    Describe more on how Donovan laid out the transect site

  • Soil Cores

    Soil cores were taken with a manual core driver (Name??). Litter was scraped off of the surface with a dull knife and the corer was hammed into the soil. Samples were measured for core length with a tape measure, placed into bags, and air-dried. Bulk density samples were taken with a (??).

    The samples were oven-dried for 24 hours and then removed. Samples were ground with a mortar and pestle to homogenize them, and poured through a 2mm sieve to remove much of the rock and debris that would skew results because of larger inorganic carbon content in rock fragments source?.

    Homogenized soil samples were run through a CN analyzer (make and model).

  • Soil survey

  • Statistical analysis

    “individual value plot of C content %”
    Shows irrigated vs drylot pastures and strata A, B, C
    95% confidence level
    ANOVA: p value of 0.865 for pastures, 0.114 for pasture by layer.
    alpha of 0.05

    “Tukey pairwise comparisons”
    at 95% confidence, difference in the means between ALL strata A, B, and C —“significantly different”
    individual confidence level 98.01%

    “Tukey pairwise comparisons pasture by layer”
    Both pastures had significantly differnet means in layer A than B and C, but B and C showed no statistical difference between them

    figures to include
    individual value plot of C content
    power curve for general full factorial
    raw data from CN analyzer?

  • Comparison

    How many samples are considered significant
    What our power and CI levels mean for baseline testing
    In 5 years, we need to:

  • Lal R., J. Kimble, E. Levine, C. Whitman. 1995. World soils and greenhouse effect: an overview. In: R. Lal, J. Kimble, E. Levine, B.A. Stewart, editors, Soils and global change. CRC Press, Boca Raton, FL. p. 1-8.

    #Lal1995

    The atmospheric sink and marine sink leave an additional 1.8 Pg C/yr unaccounted for, believed to “be absorbed by terrestrial ecosystems” (Lal et al., 1995).

    There are four pools of carbon on Earth: oceans, the atmosphere, terrestrial ecosystems, and geological formations (Lal et al., 1995).

    Soil degradation “caused by land misuse, ecologically incompatible farming systems, and inappropriate soil management practices, can be a major cause of fertility depletion and gaseous emissions from soil” (Lal et al., 1995).

    Soil degradation and desertification are critical problems in arid climate (Lal et al., 1995).

    “Science-based, economically profitable, and ecologically-sustainable agricultural systems are soil-restorative and likely to sequester carbon in world soils” (Lal et al., 1995).

    Uncertainties in data assessment “arise from unstandardized methods, data quality and reliability, and missing and incomplete data”

  • Schlesinger, W.H. 1995. An overview of the carbon cycle. In: R. Lal, J. Kimble, E. Levine, B.A. Stewart, editors, Soils and global change. CRC Press, Boca Raton, FL. p. 17.

    #Schlesinger 1995

    Small changes in carbon pools have drastic effects in the global climate system (Schlesinger, 1995).

    Losses in soil organic matter can exacerbate global warming, but increases in soil organic matter can slow the rate of atmospheric CO2 release and “provide a negative feedback” to global warming (Schlesinger, 1995).

  • #Silver et al., 2010

    Rangeland ecosystems cover half of the land area of California. “This large land area, coupled with the propensity of grasses to allocate a considerable proportion of their photosynthate belowground, leads to high soil carbon (C) sequestration potential”

    Annual grasslands typical of Mediterranean climates “differ in their life history strategies from the well-studied perennial grasslands of other regions and thus may also differ in their soil C pools and fluxes”

    Rangeland soils have been pinpointed as having high sequestration potential due to their large land coverage and ability to “drive considerable belowground allocation by rangeland plants”.

    High root biomass contributes to soil C directly through organic matter inputs and indirectly through increased soil aggregation and the formation of recalcitrant humic substances (EX QUO)

    “Regional-scale soil C analyses that include information on patterns in climate, soil type, cover type, or management allow us to explore the relative sensitivity of soil C pools to the environment and to management practices… This information can then be used to identify promising approaches and technologies for C seqeustration”

    CA rangelands differ from perennial temperate grasslands found in the Midwest. Cool wet winters and warm dry summers lead to grasslands characterized by annual grasses and forbs which die during dry, warm months and create thick surface litter that protects the soil until the wet season comes. “This life history strategy” favors lower root-shoot allocation and shallower rooting depth than perennial grasslands, as no active plant biomass occurs over the dry summer months. “could lead to lower soil C storage relative to perennial grasslands”

    In CA annual grassland, each “season’s peak aboveground biomass is equivalent to its ANPP, partially influenced by temperature, precipitation, soils, and the amount of residual dry matter”

    Grazing management in annual grasslands usually considers the relationship between RDM and ensuing year’s productivity.

    “Understanding patterns in soil C storage is a first step to exploring soil C sequestration potential”

    “The wide range in soil C pools in CA’s rangelands across similar soil types and climate suggests considerable potential to increase soil C storage in these ecosystems through management”

  • #Soussana2004

    In grasslands, three major greenhouse gases are exchanged at the atmosphere-biosphere level. Carbon dioxide is exchanged with soil and vegetation, nitrous oxide is released by soils, and methane is emitted with livestock and can be taken in by soils (Soussana et al., 2004).

    In intensive grazing systems, up to 60% of above-ground biomass is eaten by herbivores each grazing cycle (Soussana et al., 2004).

    Annual net ecosystem production of grasslands can be 1-6tC/ha/yr and is typically limited by water and/or nutrients (Soussana et al., 2004).

    Soil carbon stocks in grasslands have higher spatial variability than crop land (Soussana et al., 2004). Conversion of grassland to arable land can cause a 25-43% decline in SOC from 0-120 cm. However, converting cropland to grassland can reverse the decline and increase SOC by 0.5tC/ha/yr. Sousanna et al proposes that the rate of SOC growth in situation is slow and does not regain the level it held before the grassland was first plowed after 50 years.

    Soussana et al made four recommendations in their 2004 study. The authors recommended reducing N fertilizer inputs in highly intensive grasslands, increasing duration of grass fallows, convert fallows to grass-legume mixtures or permanent grasslands, and moderately intensifying nutrient-poor permanent grasslands (Soussana et al., 2004).

    A French study proposed that restoring half the amount of land lost since the 1970’s to permanent grassland for 20 years would be equilivalent to only 10% of France’s annual CO2 emissions from fossil fuels (Soussana et al., 2004).

    A 2004 French study utilized several modeling systems to demonstrate variabilities in a large database collected in 2002. The INRA ?? collected 19,000 unpublished references and 1000 literature references to pool data taken from the upper 30 cm of soil. The models attempted to quantify the fluxes in SOC stock and GHG changes, and generalized conclusions regarding the kinetics of SOC accumulation. The kinetics of SOC accumulation following changes in management practices appear to be non-linear and assymetric: the change is more rapid in the early years after changing land management, and accumulation is much slower than the previous release under the first management regime (Soussana et al., 2004).

  • #Batjes 1998

    The soil carbon fraction is largely associated with organic matter, but in semi-arid and arid soils, calcareous CO3-C ?? can be significant and charcoal is present in areas subject to frequent fires (Batjes 1998).

    Soil has 2.5 times more organic C than vegetation and twice the C than the atmostphere (Batjes 1998).

    The topsoil organic matter is involved in nutrient cycling and atmospheric gas exchange (Batjes 1998).

    Soil organic matter characteristics are influenced by moisture status, soil temperature, oxygen supply (drainage), soil acidity, soil nutrient supply, clay content, and mineralogy (Batjes 1998).

    The rate of turnover of organic matter can range from 15-40 years in the upper 10 cm and over 100 year for subsoil below 25 cm (Batjes 1998).

    It can take from 10 to 50 years after each disturbance to resolve a new equilibrium of soil carbon (Batjes 1998). The equilibrium established after implementation of new land management can be lower or higher than the original amount.

    Variables controlling soil C seq, like climate change and rising atmospheric levels of CO2, are “highly interactive and complex” and, simply put, there are no easy answers (Batjes 1998).

    Practices that Batjes recommends to enhance soil C seq are to account for different soil types, suitability, and factors for soil formation before cultivating or grazing land. Semi-arid grassland management can focus on reduction of burning, improving the soil nutrient status, and introducing improved grasses and legumes in combination with controlled stocking rates (Batjes 1998).

    “The role of agriculture in sequestering of organic C by soils remains ambiguous. The overall picture is complicated by technological, social, economical and cultural factors” (Batjes 1998).

    There is a historical correlation between decreases in soil carbon content and low production levels, inadequate fertilizer application, removal of crop residues, and intensive tillage practices (Batjes 1998).

  • #Soussana2010

    Grasslands cover a quarter of the earth’s land surface (Soussana et al., 2010).

    Rangelands are found on every continent and contribute to livelihoods of 800 million people. Livestock uses 3.4 billion hectares of grazing land, in addition to feed produced on a quarter of the world’s crop land (Soussana et al., 2010).

    Agricultural soils have lost an estimated 50 Gt of carbon (Soussana et al., 2010).

    Grassland soils are a major focus of carbon sequestration research, because they are typically rich in SOC. Grassland soils have active rhizodeposition and earthworm activity that promote aggregate formation that microbiota form into micro-aggregates, the form in which SOC stabilizes for extended periods (Soussana et al., 2010).

    SOC can stay in soils for hundreds of years if left undisturbed (Soussana et al., 2010).

    Native prairie soil sites in the US Great Plains were subjected to 14C-dating that found mean residence time of SOC in soil increased but the concentration decreased with depth- however, “substantial amounts of SOC” were dated back several millenia (Soussana et al., 2010).

    SOC needs protection from microbial decomposition in order to stabilized long-term. SOC in deeper soils is distanced from the energy supply from decomposing surface organic matter. When tilling mixes soil layers and breaks up soil aggregates, it also accelerates SOC decomposition and prevents stable SOC sequestration (Soussana et al., 2010).

    Soil disturbance, vegetation degradation, fire, erosion, nutrient shortage, and water deficit all lead to rapid loss of SOC (Soussana et al., 2010).

    There are two practical ways to measure or estimate SOC seq: directly by measuring changes in C pools or indirectly by measuring C fluxes. Spatial variability is the main concern that limits accuracy of direct measurements- to decrease variability, samples should be taken to different depths and avoid pastures with concentrated feces on the surface (Soussana et al., 2010).

    SOC accumulates over time in a non-linear fashion. Soussana et al estimates that converting cropland back to grassland for 20 years restores 18% of native C stocks in moist climates and 7% in temperate dry climates (Soussana et al., 2010).

    Many SOC studies focus on the 0-30cm soil strata, as most accumulation occurs in those layers, but lose can occur from deeper horizons (Soussana et al., 2010).

    Soussana et al conducted a meta-analysis of 115 studies in pastures and grazing land. They found that improved management increased SOC levels in 74% of the studies. Improved management practices included fertilization, grazing management, conversion from cultivation, and improved grass species (Soussana et al., 2010).

    An analysis of 115 studies in pastures found that light grazing increased SOC more than exclosure and heavy grazing (Soussana et al., 2010). However, the article did not specify whether the heavily grazed pastures were on a continuous or rotational grazing system.

    Nitrous oxide and methane emissions are often expressed in terms of CO2 equivalents, in an attempt to keep standard parameter (Soussana et al., 2010).

    Soil C stocks in grassland ecosystems are vulnerable to climate change (Soussana et al., 2010).

  • #Pringle et al., 2011

    Little is known about how cattle grazing affects SOC (Pringle et al., 2011).

    Pringle et al utilized linear mixed models to propose how grazing pressure and soil type affects SOC and stable carbon isotope ratio of SOC and explored the amount of soil sampling required to adequately determine baseline SOC. They found that soil type and grazing pressure interact to influence SOC to 30 cm depth. At 50 cm, there was no grazing effect but the soil type remained a significant factor. They recommended to cattle-grazing properties in tropical rangelands of Australia to divide properties into units of uniform soil type and grazing management, and use stratified simple random sampling to take 25 soil sampling locations about each unit, with at least 2 samples collected per soil stratum. They proposed that 25 soil samples per unit is adequate to estimate baseline mean SOC to within 20% of true mean to depth of 30 cm (Pringle et al., 2011).

    The substantial area of the globe devoted to grazing means that minor changes in SOC can cause proportionately large changes in C seq worldwide (Pringle et al, 2011).

    Spatial variation is further compounded by inherent soil variation, microclimate, fire history, tropography, and complex plant communities, which makes even the smallest scale of management tricky to sample precisely (Pringle et al., 2011).

    Stable carbon isotope ratio data may help to gain a more complete understanding of SOC dynamics and sequestration (Pringle et al., 2011).

  • #Pineiro et al., 2010

    “Soil organic matter is the main reservoir of SOC and soil organic nitrogen in rangelands and determines soil fertility, water retention, and soil structure” (Pineiro et al., 2010)

    In arid rangelands, SOC accumulation is limited by water availability and C uptake- also known as net primary productivity (Pineiro et al., 2010).

    Conceptual models estimate that changes in SOC stocks are determined by the balance between C and N inputs and outputs, more directly by NPP, respiration, and carbon outputs (plant production). Storage of SOC is determined by the proportion of NPP that is allocated to belowground organs. Climate, biota, time, topography, and parent materials are other factors that control SOC accumulation. Pineiro et al suggests that these contextual factors operate via cascade effects through shorter-term controls (Pineiro et al., 2010).

    A 2010 global literature review found that SOC changed under contrasted grazing conditions across climactic gradients, and that the factors that control SOC in a grazed ecosystem are more complex than we currently think they are. General patterns that the study noted were that root contents, the primary control of SOC formation, were higher in grazer than ungrazed systems at the most arid and most tropical sites but were lower at temperate sites. The increased root biomass should increase SOC because of greater C inputs to the soils (Pineiro et al., 2010).

    Grazing can change how carbon allocates in the soil. Belowground biomass enters the soil directly and contributes more to soil organic matter formation than aboveground productivity. Grazing changes the proportion of NPP allocated to aboveground or belowground organs (Pineiro et al., 2010).

    One researcher argues that grazing can affect NPP indirectly by altering species composition or soil resources by decreasing water availability (Pineiro et al., 2010).

    More efficient Nitrogen conservation can affect SOC stocks, according to Pineiro et al. The authors recommended avoiding “unwanted” N emissions from excessively loading grazing systems with nitrogen inputs, and that N dynamics would allow increased C seq in soils, and increased soil fertility (Pineiro et al., 2010).

  • #Whalen et al., 2003

    “Grazing lands contain 10-30% of the world’s SOC and have potential to act as a significant sink of atmospheric CO2” (Whalen et al., 2003).

    The Great Plains have lost 24-60% of their SOC pool from 100 years of cultivation, which breaks up soil aggregates and fragments organic matter, increasing the rate of decomposition and stimulating emission of CO2 from soils (Whalen et al., 2003).

    Crop systems have decreased C input since most above-ground biomass is removed and annual crops produce less root biomass than perennial plants (Whalen et al., 2003).

    Converting cropland to grasslands in semi-arid Great Plains don’t always work out as planned, although they can usually be restored by seeding non-native perennial grasses (Whalen et al., 2003). Understandably, total C, N, and microbial biomass are lower in recently established grasslands and can take over 50 years to approach native levels (Whalen et al., 2003).

    A crucial foundation in any system aiming to increasing SOC retention is to establish ground cover. Permanent soil cover quickly stabilizes water retention and reduces quantities of sediments, nutrients, and agricultural chemicals transported to surface waters within a few years (Whalen et al., 2003).

    EXPERIMENT: A study in the Great Plains chose 3 sites that represented 3 climactic gradients and cultivated native rangelands. In each site, plots were abandoned, seeded with non-native perennial grasses to establish permanent cover, or converted to annual crop production. Samples were obtained from 0-15 cm in depth. The soil bulk density was lower in the undisturbed native rangeland than modified plant communities, and the total C, N, and P contents declined with cultivation. The authors called for a need to collect deeper samples to determine if net gains or losses had occurred throughout the soil profile or were concentrated in the topsoil. The authors found that establishment of perennial grasses or legumes on formerly cultivated land could slow or reverse depletion of SOC, and stabilization or loss of C and N from modified plant communities is affected by climate as well as quantity and chemical characteristics of residues produced by plants (Whalen et al., 2003).

  • #Lal2004 (Lal, 2004)

    Dr. Rattan Lal recommends these strategies to increase SOC: soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands (Lal, 2004).

    The range at which C seq can offset fossil fuel emissions varies from studies depending on which modeling aspects they are focusing in on, but Dr. Rattan Lal puts the number at 0.4-1.2 Gt of carbon per year, or 5-15% of global fossil-fuel emissions (Lal, 2004).

    2500 Gt of carbon are contained in our world’s soil organic carbon pool, of which 1550 Gt is organic and 950 Gt is inorganic. In comparison, it is 3.3 times atmospheric carbon levels and 4.5 times the size of the biotic pool (Lal, 2004).

    Most global soils range from 50-150 tons per hectare of carbon in the 100 cm depth (Lal, 2004).

    Converting natural landscapes to crop production can deplete SOC by 60% in temperate regions and 75% or more in tropical climates (Lal, 2004).

    SOC loss is exaggerated in agricultural ecosystems with severe soil degradation. Carbon loss from soils is emitted directly into the atmosphere and reduces soil quality and biomass productivity, and negatively impacts water quality (Lal, 2004).

    The definition of C sequestration is the act of transferring atmospheric CO2 into long-lived pools and storing it securely in such a way that it’s not immediately reemitted (Lal, 2004). Carbon sequestration can also refer to the act of increasing the SOC pool through management practices (Lal, 2004).

    The rate of increasing SOC pools is nonlinear. Lal suggests it follows a sigmoid curve, hits the maximum rate 5-20 years after management changes and then continues until the SOC falls into equilibrium. Rates are inherently dependent on soil characteristics and climate as well as management. Dry and warm regions are subject to slower rates, upwards rates of 150 kG/ha/yr, while humid and cool climates could see C seq rates upward of 1000 kg/C/ha/year (Lal, 2004). These rates could potentially be sustained until the soil sink capacity is filled.

    Management practices that are recommended by Lal add biomass to the soil, cause minimal soil disturbance, improve soil structure, enhance soil microbiota biodiversity, and strengthen mechanisms of nutrient and water cycling (Lal, 2004).

    While C can be sequestered as secondary carbonates, that rate is low and not the subject of focus as much as SOC is (Lal, 2004).

    While soil carbon sequestration may not be the end-all of climate change solutions, it shows potential to mitigate the effects of climate change until fossil fuel alternatives take effect (Lal, 2004).

    Carbon is only one elemental constituents of humus. Sequestering 1 Gt of C in soil requires 80 Mt N, 20 Mt P, and 15 Mt K (Lal, 2004). Nutrient cycling needs to be effective for the nutrients necessary for C sequestration to be available.

    Soil erosion is a key factor in degraded land, and also removes SOC by wind and water-borne sediments transported away from the soil during erosion processes (Lal, 2004).

    Carbon markets have been in use since 2002, mostly in European Union countries. The “commodification of soil C is important for trading C credits” (Lal, 2004).

    Carbon sequestration is a bridge between 3 global issues: climate change, desertification, and biodiversity (Lal, 2004). Regardless of the climate change debate, it is a crucial issue that could increase productivity and water quality and restore degraded ecosystems (Lal, 2004).

    Agriculturally developing nations, especially those in tropical climates where dynamic soil processes exacerbate rates of SOC accumulation or loss, have the greatest need for change. Currently, the C sink capacity is high, but the rate of C seq is low and complicated by limited infrastructure and resource-poor agricultural systems (Lal, 2004).

    Generally, soil C seq by adapting recommended management practices is a natural, cost-effective, and environmentally-friendly process (Lal, 2004).

    “Soil sink capacity and performance are related to clay content and mineralogy, structural stability, landscape position, moisture and temperature regimes, and ability to form and retain stable microaggregates” (Lal, 2004).

  • #Jones2008

    If 2% of Australia’s agricultural land increased their SOC stocks by 0.5% in the top 30 cm, it would sequester the nation’s annual emissions of CO2 (Jones, 2008).

    In essence, C seq is act of storing atmospheric carbon in the soil as humified organic carbon (Jones, 2008).

    SOC can only storage permanently in wood or humus. To turn air into soil, photosynthesis converts CO2 to sugars, those simple sugars are exudated from plant roots and humification occurs in biologically active soil aggregates (Jones, 2008).

    In its most simple form, humification is joining simple carbon compounds together into more complex and stable molecules. It requires soil microbiota including mycorrhizal fungi, nitrogen fixing bacteria, and phosphorus solubilizing bacteria (Jones, 2008).

    Most conventional SOC models assume that the only C input in soils comes from biomass inputs from decomposition of surface litter and belowground roots. However, when carbon enters soil as plant material, it decomposes and is returned to the atmosphere as carbon dioxide (Jones, 2008).

    “Soluble carbon” is the idea of simple sugars from the plant being channeled into soil aggregates via the hyphae of mycorrhizal fungi, and can be rapidly stabilized by humification (Johnes, 2008).

    Mycorrhizal fungi is recognized in the agricultural world as decomposing fungi that obtains energy from decomposing organic matter and important for soil fertility and structure (Jones, 2008). Conventionally managed agricultural systems only see mycorrhizal fungi with small hyphal networks, because soil-disturbing acts like plowing and fungicide destroys the hyphae networks.

    Mycorrhizal fungi transports nutrients, including P, K, and Zn, in exchange for carbon from their plant hosts. They connect individual plants below ground and can facilitate transfer of nutrients between species (Jones, 2008).

    Humification forms a stable and inseparable part of the soil matrix that can remain intact for hundreds of years (Jones, 2008).

    Humus differs from the labile pool of soil organic carbon that forms in the topsoil. Labile carbon is formed from biomass inputs, and humified carbon is secreted from exudation from plant roots to mycorrhizal fungi and microflora, and can form deep in the soil profile (Jones, 2008).

    Considering the so-called “liquid carbon pathway”, C seq rates can range from 5-20 tCO2/ha/year (Jones, 2008).

  • #Jones2006

    Loss of ground cover, intensive cultivation, bare fallows, stubble and pasture burning, and continuous grazing are all factors that cause loss of SOC (Jones 2006).

    “Grazing animals, plants, soil biota and soils have co-evolved for over 20 million years, resulting in highly complex and sensitive inter-relationships” (Jones, 2006).

    A proposed method for how grazing soil carbon is how the plant readjusts for biomass loss after grazing. More carbon is contained in the roots than the leaves of the plant, and when the leaves are removed by grazing, and plant responds by readjusting its biomass balance. Some carbon is mobilized to the crown for production of new leaves, some is lost to the soil as root decomposition, and some is actively exuded into the rhizosphere. Thus, each grazing event becomes a “carbon injection” opportunity (Jones, 2008).

    Plants that are grazed continuously have poorly developed root systems and little C available for exudation into the soil (Jones, 2006).

  • #Waltman et al., 2010

    In the next century, the world faces a 2 degrees C or greater air temperature increased if GHG are not curtailed (Waltman et al., 2010).

    Fortunately, the agricultural sector has significant opportunities to mitigate GHG emissions, and currently one substantiated option is to increase carbon sequestration (Waltman et al., 2010).

  • #Ellert et al., 2002

    Large quantities of carbon are already present in soils, so sensitive methods are needed to detect small changes in soil C storage (Ellert et al., 2002).

    Quantitative assessments of SOC are crucial to describe ecosystem function (Ellert et al., 2002).

    SOC influences nutrient and pollutant availability, soil structure, and erosion properties (Ellert et al., 2002).

    One of the first mentions of carbon sequestration were a 1977 study that proposed C emissions could be offset by planting massive quantities of trees (Ellert et al., 2002).

    A 2002 study compared treatments in a randomized design that were treated with a known quantity of coal to compare the accuracy of soil sampling carbon measurements. The total C and N was analyzed using a CN analyzer, like our experiment. The “microsite approach” as the researchers called it, “successfully resolved small changes” in soil C storage relative to the much larger quantities already present. They did use bulk density corrections to correct for the differences in soil mass.

  • #Conant et al., 2002

    Soil carbon is tricky to detect and quantify, largely to due inherent spatial variability that limits precision the ability to detect change (Conant et al., 2002).

    Conant et al compared samples from 4 sites of unique climatic and management combinations, and found that small changes in SOC are detectable, but only with careful and controlled measurement (Conant et al., 2002).

    They found greater spatial variabilities in forested areas than cultivated sites (Conant et al., 2002).

    A 2002 study found that six cores per microplot is “adequate” to represent a range of soil samples within more uniform sites: however, this method is not appropriate for all systems (Conant et al., 2002). They recommended that multiple microplots be sampled in the future to decrease variability.

    Conant et al reommended to resample the same microplots for future measurements, as this enhances statistical power and allows changes to be detected years earlier (Conant et al., 2002).

    The minimum detectable difference is inversely related to the number of samples required (Conant et al., 2002)>

  • #DeDeyn et al., 2008

    Soil carbon storage is a key component of the global carbon cycle (De Deyn et al., 2008).

    Rapid changes can quickly make soil carbon sinks into sources for atmospheric carbon (De Deyn et al., 2008).

    NPP is determined by equilibrium between carbon input through photosynthesis, and carbon loss through plant respiration and soil respiration (De Deyn et al., 2008).

    Non-respiratory losses of carbon include decomposition processes, charring or burning, and volatilization and leaching or organic compounds (De Deyn et al., 2008).

    It is thought that the maximum sequestration potential of soils is determined by intrinsic abiotic soil factors like topography, mineralogy, and texture, and that biota-driven factors are a minor factor in soil carbon dynamics (De Deyn et al., 2008).

    General plant traits regulate SOC by altering carbon input through NPP and belowground carbon allocation (De Deyn et al., 2008).

    Fast-growing plant species contribute carbon through root exudate to the soil, while slow-growing species contribute through input of low quality plant material. In biomes with a short growing season and low nutrient availability, SOC input is mainly derived from litter decomposition, but in productive biomes NPP is the main driver of carbon sequestration (De Deyn et al., 2008).

    Mycorrhizal fungi and nitrogen fixing bacteria are common plant symbionts that can increase plant productivity by attaining and transfering resources (De Deyn et al., 2008).

    MF enhances plant nutrient acquisition from soil, reduces soil C loss by immobilizing carbon in the myeclium, extending root lifespan, and importing C to soil aggregates, and are conveniently associated with most terrestrial plant species (De Deyn et al., 2008).

    “Long term enhancement of SOC seq requires sustained primary productivity and efficient feedback between communities of plants and soil biota for carbon and nutrient cycling” (De Deyn et al., 2008).

    Maximizing the balance between soil carbon input and output is the best way to enhance SOC seq (De Deyn et al., 2008).

    De Deyn et al states that we don’t yet know enough about the link s between aboveground and belowground plant traits to be able to make accurate predictions about impact on SOC seq or response to global change (De Deyn et al., 2008).

    The scientific community needs to be open to new plant traits and pathways of carbon flow, as we discover more about soil microbiota and their ecosystems (De Deyn et al., 2008).

  • #Jastrow et al., 2007

    Jastrow et al recommend reducing C turnover and increasing residence time in soils to maximize soil C seq (Jastrow et al., 2007).

    Biochemical alteration is the process of transforming SOC to chemical forms that are more resistant to decomposition and are incorporated into soil solids (Jastrow et al., 2007).

    Physicochemical protection is the ability of organomineral interactions to protect SOC from biochemical attack (decomposition) (Jastrow et al., 2007).

    There are several ways to stabilize SOC to protect it from decomposition. These include occluding SOC within aggregates, depositing it in pores inaccessible to decomposers, and sorption ?? to mineral and organic soil surfaces (Jastrow et al., 2007).

    Changing management practices to those that shift the soil biochemical environment to favor fungi can reduce the rates of SOC decomposition and enhance sequestration. Practices that show potential for accomplishing this include planting perennial species, reducing tillage, maintaining neutral soil pH, ensuring adequate drainage, and minimizing erosion (Jastrow et al., 2007).

  • #Donovan2013 (Donovan, 2013)

    “Soil carbon measurement is as much a social issue, involving beliefs and attitudes, as it is a technical one” (Donovan, 2013)

    The global issue of carbon has many contexts and perceptions, as well as different uses to people and producers (Donovan, 2013). This complicates the seemingly simple idea of measuring soil carbon change.

    “Carbon is life and food, and moves from atmosphere to plants and soils and back in a grand cycle that is sometimes called the circle of life” (Donovan, 2013).

    Peter Donovan, creator of the Soil Carbon Coalition, writes that “soil carbon may be one of the easiest and most practical ways to monitor the work of the biosphere on land” (Donovan, 2013).

    The major sources of uncertainty in SOC sampling is sampling error and non-random selection of sampling sites (Donovan 2013).

    To maximize the chance of detecting and measuring change, Donovan recommends waiting longer between samplings (Donovan, 2013). This would also aid to distinguish between year-to-year weather variability (Donovan, 2013).

    There are 3 forms of carbon in soil. The largest fraction is organic soil carbon, which is derived from living tissue. It is critical in the formation of soil aggregates but is typically the least stable form of carbon. Charcoal is derived from living tissue as well, so is considered organic and is also more resistant to decomposition. Inorganic soil carbon is the most stable form because it is protected from decomposition but typically changes at a slower rate (Donovan, 2013).

    Donovan lists 5 laboratory techniques to measure soil carbon directly from soil samples. These include elemental analysis by dry combustion, acid treatments, loss on ignition, carbon fractions, and soil respiration. Of these, elemental analysis by dry combustion is considered the most accurate that is likely to detect change in the organic carbon fraction but measures total soil carbon (inorganic and organic) (Donovan, 2013).

    Sampling from different horizontal strata reduces variability since deeper layers have less spatiotemporal variation and can help to account for differences in soil types, vegetation cover, management, etc. (Donovan, 2013).

    MASS OF CARBON: TOTAL CARBON = FRACTION CARBON (DECIMAL) X DENSITY X VOLUME IN CUBIC METERS

    STANDARD ERROR= STANDARD DEVIATION OF ALL SAMPLES DIVIDED BY SQUARE ROOT OF NUMBER OF SOIL CORES

    Testing microsites to make broad conclusions about a pasture’s soil carbon content is analogous to comparing three tax returns in a small town to gain an accurate view of the average personal income (Donovan, 2013).

  • #Lal2007
    (Lal et al., 2007)

    The definition of carbon sequestration, according to the Department of Energy, is “the provision of long-term storage of carbon in the terrestrial biosphere, underground, or the oceans so that the build-up of CO2 will reduce or slow”. Sequestration is either natural or anthropogenic-driven. Natural sequestration is limited to terrestrial sequestration in soil and trees, while anthropogenic-driven geologic sequestration include such man-made technologies as injection of liquified CO2 into rock formations, old oil wells, etc. (Lal et al., 2007).

    Soil quality is defined as the combination of characteristics that enable soils to perform a wide range of functions (Lal et al., 2007).

    Management choices affect the amount of soil organic matter, soil structure, soil depth, and water and nutrient-holding capacity (Lal et al., 2007).

    Pastures and rangelands cover 55% of United States’s total land surface, and represent the largest and most diverse resource in the world (Lal et al., 2007).

    The SOC seq potential for US cropland and grazing land is 180Mt SOC/yr (Lal et al., 2007).

  • #Fynn et al., 2010

    The term “rangelands” includes grasses, savannas, steppes, shrub lands, desert, and tundra (Fynn et al., 2010).

    A small change in SOC could have a large impact on overall GHG, since US rangelands represent such a large surface area (Fynn et al., 2010).

    US grazing lands could potentially sequester up to 198 million t CO2 /yr from atmosphere for 30 years (Fynn et al., 2010).

    Each ton of C stored in soils removes 3.67 t of CO2 from the atmosphere (Fynn et al., 2010).

    SOC is 50% of soil organic matter (Fynn et al., 2010).

    Management recommendations made by Flynn et al for increased carbon sequestration include adjustments in stocking rates, introduction of grasses on degraded lands, managing invasive species, reseeding grassland species, riparian zone restoration, and introduction of biochar to soils (Fynn et al., 2010).

    The basic idea of a “carbon market” is to instill a financial incentive to producers to sequester soil organic carbon on their land. Increased soil carbon levels would be converted to verified emissions reductions to use within an offset market, cap and trade system, or other credit program (Fynn et al., 2010).

    In terms of sampling, accuracy costs more and cheaper methods are traditionally less accurate (Fynn et al., 2010).

    “Rather than tie a protocol to the limitations of one particular method, it is logical to combine the strengths of different methods into a single methodology, which may be updated as economics and technical advances allow” (fynn et al., 2010).

    Carbon enters the plant from the atmosphere, and becomes soil carbon through processes of above and below-ground decomposition, root decomposition, and the release of exudates from plant roots in the soil (Fynn et al., 2010).

    90% of carbon in rangeland systems is in the soil (Fynn et al., 2010).

    SOC accumulation is directly correlated to precipitation and inversely correlated to temperature (Fynn et al., 2010).

    There are 3 major ways to protect soil organic carbon from microbial decomposition. Chemical stabilization is the bonding of positively charged SOC molecules to negatively charged iron and clay anions. Physical protection is holding soil aggregates together with “glues” like glomalin, and biochemical recalcitrance is characteristics of carbon substrates that are consumed by microbes but remain un-decayed compounds (Fynn et al., 2010).

    Two types of carbon in each accumulated pool have different mean residence times. The light fraction, made of fresh plant materials subject to rapid decomposition, turnover within a few years at most. Early changes in SOC from management changes occur in this fraction, which is also known for its high spatiotemporal variability. The heavily occluded fraction, composed of carbohydrates and humic materials stabilized in clay complexes, can remain in soil for hundreds to over a thousand years (Fynn et al., 2010).

    Typically, soils accumulated carbon during plant growth and lose carbon during dormancy (Fynn et al., 2010).

    13.6 million acres make up California annual grasslands, which subdivide into inland valley grassland, coastal prairie, and coast range grassland. The plant communities are now dominated by exotic annual grasses brought from Mediterranean regions by Spanish explorers (Fynn et al., 2010).

    A rangeland soil carbon sampling methodology should use several methods in combination, which can be placed along a spectrum with practicality at the cheapest end and high confidence levels at the expensive end (Fynn et al., 2010).

    The challenge in determining how management practices affect soil carbon sequestration lies in determining the relationships among precipitation, stocking rate, and carbon dynamics (Fynn et al., 2010).

    Variability in sampling can be minimized by lengthening the time between samplings, or increasing the space between samples to cover more of the landscape (Fynn et al., 2010)>

    Direct methods of SOC measure directly from a soil sample, while indirect methods rely on modeling to predict the relationship between variable and carbon content (Fynn et al., 2010),

    Three uses of indirect measurement methods may assist in verifying direct measurement findings. They include the use of process-based or mechanistic models, remote sensing via satellite, and land use history and databases (Fynn et al., 2010).

  • #Friedman et al., 2001

    Improving soil quality is crucial to achievement of water quality, air quality, and carbon sequestration goals (Friedman et al., 2001).

    Usually, testing for soil quality includes a minimum data set that utilizes indicators of microbial biomass C and N (Friedman et al., 2001).

  • #NRCS1996

    “Rangelands trap and store carbon and thus reduce atmospheric greenhouse gases, store water, and filter impurities from water” (NRCS, 1996).

    America’s rangelands deteriorated rapidly and significantly during the late 1800s (NRCS, 1996).

  • ##distinction between C seq and C pools... where to put?

    There is a semantic distinction between the terms “carbon sequestration” and “soil carbon pool”. The soil organic pool is a measurement of carbon in a depth of soil at any given time, while sequestration refers to the act of pulling in carbon and storing it into the soils. Soil carbon pools can be thought of a single “snapshot” in a dynamic process of carbon sequestration.

  • Climate Change- broad impact statement

    In the next century, the world faces a 2 degrees C or greater air temperature increased if GHG are not curtailed (Waltman et al., 2010).
    Fortunately, the agricultural sector has significant opportunities to mitigate GHG emissions, and currently one substantiated option is to increase carbon sequestration (Waltman et al., 2010).

    The agriculture, forestry, and other land use sector contributes just under a quarter of anthropogenic GHG emissions, or 10-12Gt CO2 eq/year (Smith et al., 2014).
    The agricultural sector is the largest contribute to global anthropogenic non-CO2 GHG at 56% in 2005- not including agricultural machinery use. Between 1990 and 2010, agricultural non-CO2 emissions grew by 0.9%/year (Smith et al,. 2014).
    Eneteric fermentation and agricultural soils contribute to 70% of total agricultural emissions. Biomass burning accounts for 6-12%, and synethetic fertilization to 12% (Smith et al., 2014).

    The International Panel on Climate Change predicts that the supply of primary energy will be dominated by fossil fuels until at least 2050 (IPCC, 2005).

    The Lima-Paris Action Agenda, unveiled at the United Nation Climate Change Conference in November 2015, announced that the carbon farming movement is “moving forwards”. Targeting the Action Agenda’s goal of resilient societies with low carbon levels, it stated that a “growing” number of advocates say that “one of the best opportunities for drawing carbon back to Earth is for its land managers to sequester more carbon in the soil” (Bland, 2015).

  • #Smith et al., 2014

    The agriculture, forestry, and other land use sector contributes just under a quarter of anthropogenic GHG emissions, or 10-12Gt CO2 eq/year (Smith et al., 2014).

    The agricultural sector is the largest contribute to global anthropogenic non-CO2 GHG at 56% in 2005- not including agricultural machinery use. Between 1990 and 2010, agricultural non-CO2 emissions grew by 0.9%/year (Smith et al,. 2014).

    Eneteric fermentation and agricultural soils contribute to 70% of total agricultural emissions. Biomass burning accounts for 6-12%, and synethetic fertilization to 12% (Smith et al., 2014).

  • Definition of carbon sequestration

    Agricultural soils have lost an estimated 50 Gt of carbon (Soussana et al., 2010).

    The range at which C seq can offset fossil fuel emissions varies from studies depending on which modeling aspects they are focusing in on, but Dr. Rattan Lal puts the number at 0.4-1.2 Gt of carbon per year, or 5-15% of global fossil-fuel emissions (Lal, 2004).

    2500 Gt of carbon are contained in our world’s soil organic carbon pool, of which 1550 Gt is organic and 950 Gt is inorganic. In comparison, it is 3.3 times atmospheric carbon levels and 4.5 times the size of the biotic pool (Lal, 2004).

    Most global soils range from 50-150 tons per hectare of carbon in the 100 cm depth (Lal, 2004).

    The definition of C sequestration is the act of transferring atmospheric CO2 into long-lived pools and storing it securely in such a way that it’s not immediately reemitted (Lal, 2004). Carbon sequestration can also refer to the act of increasing the SOC pool through management practices (Lal, 2004).

    Carbon sequestration is a bridge between 3 global issues: climate change, desertification, and biodiversity (Lal, 2004). Regardless of the climate change debate, it is a crucial issue that could increase productivity and water quality and restore degraded ecosystems (Lal, 2004).

    Agriculturally developing nations, especially those in tropical climates where dynamic soil processes exacerbate rates of SOC accumulation or loss, have the greatest need for change. Currently, the C sink capacity is high, but the rate of C seq is low and complicated by limited infrastructure and resource-poor agricultural systems (Lal, 2004).

    Generally, soil C seq by adapting recommended management practices is a natural, cost-effective, and environmentally-friendly process (Lal, 2004).

    In essence, C seq is act of storing atmospheric carbon in the soil as humified organic carbon (Jones, 2008).

    One of the first mentions of carbon sequestration were a 1977 study that proposed C emissions could be offset by planting massive quantities of trees (Ellert et al., 2002).

    Soil carbon storage is a key component of the global carbon cycle (De Deyn et al., 2008).

    Definition carbon seq continued

    It is thought that the maximum sequestration potential of soils is determined by intrinsic abiotic soil factors like topography, mineralogy, and texture, and that biota-driven factors are a minor factor in soil carbon dynamics (De Deyn et al., 2008).

    “Soil carbon measurement is as much a social issue, involving beliefs and attitudes, as it is a technical one” (Donovan, 2013)
    The global issue of carbon has many contexts and perceptions, as well as different uses to people and producers (Donovan, 2013). This complicates the seemingly simple idea of measuring soil carbon change.
    “Carbon is life and food, and moves from atmosphere to plants and soils and back in a grand cycle that is sometimes called the circle of life” (Donovan, 2013).

    Eneteric fermentation and agricultural soils contribute to 70% of total agricultural emissions. Biomass burning accounts for 6-12%, and synethetic fertilization to 12% (Smith et al., 2014).

    The definition of carbon sequestration, according to the Department of Energy, is “the provision of long-term storage of carbon in the terrestrial biosphere, underground, or the oceans so that the build-up of CO2 will reduce or slow”. Sequestration is either natural or anthropogenic-driven. Natural sequestration is limited to terrestrial sequestration in soil and trees, while anthropogenic-driven geologic sequestration include such man-made technologies as injection of liquified CO2 into rock formations, old oil wells, etc. (Lal et al., 2007).
    Soil quality is defined as the combination of characteristics that enable soils to perform a wide range of functions (Lal et al., 2007).
    Management choices affect the amount of soil organic matter, soil structure, soil depth, and water and nutrient-holding capacity (Lal et al., 2007).

    The definition of C sequestration is the act of transferring atmospheric CO2 into long-lived pools and storing it securely in such a way that it’s not immediately reemitted (Lal, 2004). Carbon sequestration can also refer to the act of increasing the SOC pool through management practices (Lal, 2004).

    US grazing lands could potentially sequester up to 198 million t CO2 /yr from atmosphere for 30 years (Fynn et al., 2010).

    Each ton of C stored in soils removes 3.67 t of CO2 from the atmosphere (Fynn et al., 2010).

  • Grasslands and carbon sequestration

    Annual net ecosystem production of grasslands can be 1-6tC/ha/yr and is typically limited by water and/or nutrients (Soussana et al., 2004).

    Grasslands cover a quarter of the earth’s land surface (Soussana et al., 2010).
    Rangelands are found on every continent and contribute to livelihoods of 800 million people. Livestock uses 3.4 billion hectares of grazing land, in addition to feed produced on a quarter of the world’s crop land (Soussana et al., 2010).

    Agricultural soils have lost an estimated 50 Gt of carbon (Soussana et al., 2010).

    Grassland soils are a major focus of carbon sequestration research, because they are typically rich in SOC. Grassland soils have active rhizodeposition and earthworm activity that promote aggregate formation that microbiota form into micro-aggregates, the form in which SOC stabilizes for extended periods (Soussana et al., 2010).

    “Grazing lands contain 10-30% of the world’s SOC and have potential to act as a significant sink of atmospheric CO2” (Whalen et al., 2003).
    The Great Plains have lost 24-60% of their SOC pool from 100 years of cultivation, which breaks up soil aggregates and fragments organic matter, increasing the rate of decomposition and stimulating emission of CO2 from soils (Whalen et al., 2003).
    Crop systems have decreased C input since most above-ground biomass is removed and annual crops produce less root biomass than perennial plants (Whalen et al., 2003).
    Converting cropland to grasslands in semi-arid Great Plains don’t always work out as planned, although they can usually be restored by seeding non-native perennial grasses (Whalen et al., 2003). Understandably, total C, N, and microbial biomass are lower in recently established grasslands and can take over 50 years to approach native levels (Whalen et al., 2003).

    “Soil organic matter is the main reservoir of SOC and soil organic nitrogen in rangelands and determines soil fertility, water retention, and soil structure” (Pineiro et al., 2010)
    In arid rangelands, SOC accumulation is limited by water availability and C uptake- also known as net primary productivity (Pineiro et al., 2010).

    “Rangelands trap and store carbon and thus reduce atmospheric greenhouse gases, store water, and filter impurities from water” (NRCS, 1996).
    America’s rangelands deteriorated rapidly and significantly during the late 1800s (NRCS, 1996).

    Pastures and rangelands cover 55% of United States’s total land surface, and represent the largest and most diverse resource in the world (Lal et al., 2007).

    The SOC seq potential for US cropland and grazing land is 180Mt SOC/yr (Lal et al., 2007).

    13.6 million acres make up California annual grasslands, which subdivide into inland valley grassland, coastal prairie, and coast range grassland. The plant communities are now dominated by exotic annual grasses brought from Mediterranean regions by Spanish explorers (Fynn et al., 2010).

    The term “rangelands” includes grasses, savannas, steppes, shrub lands, desert, and tundra (Fynn et al., 2010).
    A small change in SOC could have a large impact on overall GHG, since US rangelands represent such a large surface area (Fynn et al., 2010).
    US grazing lands could potentially sequester up to 198 million t CO2 /yr from atmosphere for 30 years (Fynn et al., 2010).
    Each ton of C stored in soils removes 3.67 t of CO2 from the atmosphere (Fynn et al., 2010).
    SOC is 50% of soil organic matter (Fynn et al., 2010).
    Management recommendations made by Flynn et al for increased carbon sequestration include adjustments in stocking rates, introduction of grasses on degraded lands, managing invasive species, reseeding grassland species, riparian zone restoration, and introduction of biochar to soils (Fynn et al., 2010).

    90% of carbon in rangeland systems is in the soil (Fynn et al., 2010).

    In grasslands, three major greenhouse gases are exchanged at the atmosphere-biosphere level. Carbon dioxide is exchanged with soil and vegetation, nitrous oxide is released by soils, and methane is emitted with livestock and can be taken in by soils (Soussana et al., 2004).

  • Biomechanics: 3 ways of natural sequestration

    While C can be sequestered as secondary carbonates, that rate is low and not the subject of focus as much as SOC is (Lal, 2004).
    While soil carbon sequestration may not be the end-all of climate change solutions, it shows potential to mitigate the effects of climate change until fossil fuel alternatives take effect (Lal, 2004).

    Many SOC studies focus on the 0-30cm soil strata, as most accumulation occurs in those layers, but lose can occur from deeper horizons (Soussana et al., 2010).

    Soil has 2.5 times more organic C than vegetation and twice the C than the atmostphere (Batjes 1998).

    The topsoil organic matter is involved in nutrient cycling and atmospheric gas exchange (Batjes 1998).

    Soil organic matter characteristics are influenced by moisture status, soil temperature, oxygen supply (drainage), soil acidity, soil nutrient supply, clay content, and mineralogy (Batjes 1998).

    General plant traits regulate SOC by altering carbon input through NPP and belowground carbon allocation (De Deyn et al., 2008).

    Fast-growing plant species contribute carbon through root exudate to the soil, while slow-growing species contribute through input of low quality plant material. In biomes with a short growing season and low nutrient availability, SOC input is mainly derived from litter decomposition, but in productive biomes NPP is the main driver of carbon sequestration (De Deyn et al., 2008).

    There are 3 forms of carbon in soil. The largest fraction is organic soil carbon, which is derived from living tissue. It is critical in the formation of soil aggregates but is typically the least stable form of carbon. Charcoal is derived from living tissue as well, so is considered organic and is also more resistant to decomposition. Inorganic soil carbon is the most stable form because it is protected from decomposition but typically changes at a slower rate (Donovan, 2013).

    It is thought that the maximum sequestration potential of soils is determined by intrinsic abiotic soil factors like topography, mineralogy, and texture, and that biota-driven factors are a minor factor in soil carbon dynamics (De Deyn et al., 2008).

  • Biomechanics: Longevity & protecting from decomposition

    Soil carbon stocks in grasslands have higher spatial variability than crop land (Soussana et al., 2004). Conversion of grassland to arable land can cause a 25-43% decline in SOC from 0-120 cm. However, converting cropland to grassland can reverse the decline and increase SOC by 0.5tC/ha/yr. Sousanna et al proposes that the rate of SOC growth in situation is slow and does not regain the level it held before the grassland was first plowed after 50 years.

    SOC accumulates over time in a non-linear fashion. Soussana et al estimates that converting cropland back to grassland for 20 years restores 18% of native C stocks in moist climates and 7% in temperate dry climates (Soussana et al., 2010).

    The rate of turnover of organic matter can range from 15-40 years in the upper 10 cm and over 100 year for subsoil below 25 cm (Batjes 1998).

    It can take from 10 to 50 years after each disturbance to resolve a new equilibrium of soil carbon (Batjes 1998). The equilibrium established after implementation of new land management can be lower or higher than the original amount.

    Variables controlling soil C seq, like climate change and rising atmospheric levels of CO2, are “highly interactive and complex” and, simply put, there are no easy answers (Batjes 1998).

    SOC can stay in soils for hundreds of years if left undisturbed (Soussana et al., 2010).

    Native prairie soil sites in the US Great Plains were subjected to 14C-dating that found mean residence time of SOC in soil increased but the concentration decreased with depth- however, “substantial amounts of SOC” were dated back several millenia (Soussana et al., 2010).

    SOC needs protection from microbial decomposition in order to stabilized long-term. SOC in deeper soils is distanced from the energy supply from decomposing surface organic matter. When tilling mixes soil layers and breaks up soil aggregates, it also accelerates SOC decomposition and prevents stable SOC sequestration (Soussana et al., 2010).

    The rate of increasing SOC pools is nonlinear. Lal suggests it follows a sigmoid curve, hits the maximum rate 5-20 years after management changes and then continues until the SOC falls into equilibrium. Rates are inherently dependent on soil characteristics and climate as well as management. Dry and warm regions are subject to slower rates, upwards rates of 150 kG/ha/yr, while humid and cool climates could see C seq rates upward of 1000 kg/C/ha/year (Lal, 2004). These rates could potentially be sustained until the soil sink capacity is filled.

    Biochemical alteration is the process of transforming SOC to chemical forms that are more resistant to decomposition and are incorporated into soil solids (Jastrow et al., 2007).

    Physicochemical protection is the ability of organomineral interactions to protect SOC from biochemical attack (decomposition) (Jastrow et al., 2007).

    There are several ways to stabilize SOC to protect it from decomposition. These include occluding SOC within aggregates, depositing it in pores inaccessible to decomposers, and sorption ?? to mineral and organic soil surfaces (Jastrow et al., 2007).

    There are 3 major ways to protect soil organic carbon from microbial decomposition. Chemical stabilization is the bonding of positively charged SOC molecules to negatively charged iron and clay anions. Physical protection is holding soil aggregates together with “glues” like glomalin, and biochemical recalcitrance is characteristics of carbon substrates that are consumed by microbes but remain un-decayed compounds (Fynn et al., 2010).

    Two types of carbon in each accumulated pool have different mean residence times. The light fraction, made of fresh plant materials subject to rapid decomposition, turnover within a few years at most. Early changes in SOC from management changes occur in this fraction, which is also known for its high spatiotemporal variability. The heavily occluded fraction, composed of carbohydrates and humic materials stabilized in clay complexes, can remain in soil for hundreds to over a thousand years (Fynn et al., 2010).
    Typically, soils accumulated carbon during plant growth and lose carbon during dormancy (Fynn et al., 2010).

  • Variability: Models

    A 2004 French study utilized several modeling systems to demonstrate variabilities in a large database collected in 2002. The INRA ?? collected 19,000 unpublished references and 1000 literature references to pool data taken from the upper 30 cm of soil. The models attempted to quantify the fluxes in SOC stock and GHG changes, and generalized conclusions regarding the kinetics of SOC accumulation. The kinetics of SOC accumulation following changes in management practices appear to be non-linear and assymetric: the change is more rapid in the early years after changing land management, and accumulation is much slower than the previous release under the first management regime (Soussana et al., 2004).

    Conceptual models estimate that changes in SOC stocks are determined by the balance between C and N inputs and outputs, more directly by NPP, respiration, and carbon outputs (plant production). Storage of SOC is determined by the proportion of NPP that is allocated to belowground organs. Climate, biota, time, topography, and parent materials are other factors that control SOC accumulation. Pineiro et al suggests that these contextual factors operate via cascade effects through shorter-term controls (Pineiro et al., 2010).

    Most conventional SOC models assume that the only C input in soils comes from biomass inputs from decomposition of surface litter and belowground roots. However, when carbon enters soil as plant material, it decomposes and is returned to the atmosphere as carbon dioxide (Jones, 2008).

    Direct methods of SOC measure directly from a soil sample, while indirect methods rely on modeling to predict the relationship between variable and carbon content (Fynn et al., 2010),

    Three uses of indirect measurement methods may assist in verifying direct measurement findings. They include the use of process-based or mechanistic models, remote sensing via satellite, and land use history and databases (Fynn et al., 2010).

  • #Lara et al., nd

    Quantifying “ecosystem services” is a complex and convoluted process, albeit necessary to quantify the value to human societies that natural capital resources bring. Modern agriculture is a “major driver of global environment change” and there are numerous efforts to establish sophisticated economic models to predict global effects of carbon sequestration efforts. These include ARIES (artificial intelligence for ecosystem services) which takes open source data into account, InVEST (integrated valuation of ecosystem services and tradeoffs) which provides maps of monetary value among other outputs, and MAgPIE (Model of agricultural production and its impact on the environment) which shows potential output of carbon storage in soils and crop residue, etc (Lara et al, nd). These are just a few of numerous modeling systems that could be of future use towards establishing a global or domestic carbon market.

  • Variability: Spatiotemporal

    Soil carbon stocks in grasslands have higher spatial variability than crop land (Soussana et al., 2004). Conversion of grassland to arable land can cause a 25-43% decline in SOC from 0-120 cm. However, converting cropland to grassland can reverse the decline and increase SOC by 0.5tC/ha/yr. Sousanna et al proposes that the rate of SOC growth in situation is slow and does not regain the level it held before the grassland was first plowed after 50 years.

    Spatial variation is further compounded by inherent soil variation, microclimate, fire history, tropography, and complex plant communities, which makes even the smallest scale of management tricky to sample precisely (Pringle et al., 2011).

    Soil carbon is tricky to detect and quantify, largely to due inherent spatial variability that limits precision the ability to detect change (Conant et al., 2002).

    Conant et al compared samples from 4 sites of unique climatic and management combinations, and found that small changes in SOC are detectable, but only with careful and controlled measurement (Conant et al., 2002).

    They found greater spatial variabilities in forested areas than cultivated sites (Conant et al., 2002).

    The major sources of uncertainty in SOC sampling is sampling error and non-random selection of sampling sites (Donovan 2013).

    To maximize the chance of detecting and measuring change, Donovan recommends waiting longer between samplings (Donovan, 2013). This would also aid to distinguish between year-to-year weather variability (Donovan, 2013).

  • Mycorrhizal/Humification

    In its most simple form, humification is joining simple carbon compounds together into more complex and stable molecules. It requires soil microbiota including mycorrhizal fungi, nitrogen fixing bacteria, and phosphorus solubilizing bacteria (Jones, 2008).

    “Soluble carbon” is the idea of simple sugars from the plant being channeled into soil aggregates via the hyphae of mycorrhizal fungi, and can be rapidly stabilized by humification (Johnes, 2008).

    Mycorrhizal fungi is recognized in the agricultural world as decomposing fungi that obtains energy from decomposing organic matter and important for soil fertility and structure (Jones, 2008). Conventionally managed agricultural systems only see mycorrhizal fungi with small hyphal networks, because soil-disturbing acts like plowing and fungicide destroys the hyphae networks.

    Mycorrhizal fungi transports nutrients, including P, K, and Zn, in exchange for carbon from their plant hosts. They connect individual plants below ground and can facilitate transfer of nutrients between species (Jones, 2008).
    Humification forms a stable and inseparable part of the soil matrix that can remain intact for hundreds of years (Jones, 2008).

    Humus differs from the labile pool of soil organic carbon that forms in the topsoil. Labile carbon is formed from biomass inputs, and humified carbon is secreted from exudation from plant roots to mycorrhizal fungi and microflora, and can form deep in the soil profile (Jones, 2008).

    Considering the so-called “liquid carbon pathway”, C seq rates can range from 5-20 tCO2/ha/year (Jones, 2008).

    Mycorrhizal fungi and nitrogen fixing bacteria are common plant symbionts that can increase plant productivity by attaining and transfering resources (De Deyn et al., 2008).

    MF enhances plant nutrient acquisition from soil, reduces soil C loss by immobilizing carbon in the myeclium, extending root lifespan, and importing C to soil aggregates, and are conveniently associated with most terrestrial plant species (De Deyn et al., 2008).

  • #Leake et al., 2004

    One study refers to mycorrhizal fungi as the “most dynamic and functionally diverse components of symbiosis” (Leake et al., 2004).

    Mycorrhizal fungi can constitute 20-30% of the total soil microbial biomass, but are not detected by standard measures of biomass (Leake et al., 2004).

    Some plants depend exclusively on MF for carbon (Leake et al., 2004).

    MF are highly sensitive to soil disturbance, and so the process to observe MF is difficult and complicated (Leake et al., 2004).

    MF gain direct access to plant-exudated sugars, giving it energy “unparalleled” amongst soil microbiota populations (Leake et al., 2004).

    “most recent models of C fluxes between herbaceous plants and soil have been based upon the assumption that root exudation, sloughed cells and dead roots provide the only significant pathway for the supply of plant-fixed C to the free-living microbial populations in soils” (Leake et al., 2004).

    One estimate suggests that as much as 15% of SOC stock is contributed by arbuscular mycorrhizal fungi (Leake et al., 2004).

    Arbuscular mycorrhizal fungi secrete glomalin that accumulates in soil, contributing substantial amounts of stable SOC (Leake et al., 2004).

    The structural complexity of mycelial network pathways have only recently been discovered (Leake et al., 2004).

    “Mycorrhizal networks can contribute to sustainability by increasing nutrient-use efficiency, reducing infections by root pathogens, and increasing soil-aggregate stability and soil physical properties” (Leake et al., 2004).

    Generally stated, MF hyphae carry carbohydrates from plants into soil regions far beyond the conventional rhizosphere and release exudates and other compounds to interact with soil microbiota (Leake et al., 2004).

  • #Allen 2006

    The effects of mycorrhizal fungi on soil physical structure and water flow are poorly understood, as before now the focus has been on their ability for increasing nutrient uptake from soils (Allen, 2006).

    Individual fungal hyphae may be 2-10 micrometers in diameter but can extends across many hectares, penetrating soil pores to increase pathways for water flow and conductivity (Allen, 2006).

    There can be several kilometers of hyphae present in a single gram of soil (Allen, 2006).

    Mycorrhizal fungi typically acquire 10-30% of the plant’s net carbon fixation and turn it over to hyphae in hours to days (Allen, 2006).

    Mycorrhizal fungi are best known for their ability to take up and transport nutrients to the host plant in exchange for the plant’s C (Allen, 2006).

    Annual, tilled croplands subject to intensive fertilization and herbicide application have lost or dramatically reduced mycorrhizal fungi, therefore the properties of water movement are changed in these environments (Allen, 2006).

    It can take several years for a newly established perennial system to establish a developed network of mycorrhizal fungi (Allen, 2006).

  • #Spaccini et al., 2002

    Humified SOC can have an average residence time of several hundreds of years (Spaccini et al., 2002).

    We used to think humic substances were huge polymers, but now we understand that they are associations of small molecules held together by weak forces, and interact closely with organic compounds in the soil (Spaccini et al., 2002).

    One experiment found that addition of humid acids to soil significantly increased organic carbon sequestration, and confirmed the association between fine soil textural fractions and organic matter in soils (Spaccini et al., 2002).

    Sequestration of carbon into the humic pool protects it by mineralization from microbial degradation (Spaccini et al., 2002).

  • Different ways of direct measurement

    There are two practical ways to measure or estimate SOC seq: directly by measuring changes in C pools or indirectly by measuring C fluxes. Spatial variability is the main concern that limits accuracy of direct measurements- to decrease variability, samples should be taken to different depths and avoid pastures with concentrated feces on the surface (Soussana et al., 2010).

    SOC accumulates over time in a non-linear fashion. Soussana et al estimates that converting cropland back to grassland for 20 years restores 18% of native C stocks in moist climates and 7% in temperate dry climates (Soussana et al., 2010).

    Many SOC studies focus on the 0-30cm soil strata, as most accumulation occurs in those layers, but lose can occur from deeper horizons (Soussana et al., 2010).

    Donovan lists 5 laboratory techniques to measure soil carbon directly from soil samples. These include elemental analysis by dry combustion, acid treatments, loss on ignition, carbon fractions, and soil respiration. Of these, elemental analysis by dry combustion is considered the most accurate that is likely to detect change in the organic carbon fraction but measures total soil carbon (inorganic and organic) (Donovan, 2013).

  • Sample Size

    Pringle et al utilized linear mixed models to propose how grazing pressure and soil type affects SOC and stable carbon isotope ratio of SOC and explored the amount of soil sampling required to adequately determine baseline SOC. They found that soil type and grazing pressure interact to influence SOC to 30 cm depth. At 50 cm, there was no grazing effect but the soil type remained a significant factor. They recommended to cattle-grazing properties in tropical rangelands of Australia to divide properties into units of uniform soil type and grazing management, and use stratified simple random sampling to take 25 soil sampling locations about each unit, with at least 2 samples collected per soil stratum. They proposed that 25 soil samples per unit is adequate to estimate baseline mean SOC to within 20% of true mean to depth of 30 cm (Pringle et al., 2011).

    Large quantities of carbon are already present in soils, so sensitive methods are needed to detect small changes in soil C storage (Ellert et al., 2002).

    Quantitative assessments of SOC are crucial to describe ecosystem function (Ellert et al., 2002).

    A 2002 study compared treatments in a randomized design that were treated with a known quantity of coal to compare the accuracy of soil sampling carbon measurements. The total C and N was analyzed using a CN analyzer, like our experiment. The “microsite approach” as the researchers called it, “successfully resolved small changes” in soil C storage relative to the much larger quantities already present. They did use bulk density corrections to correct for the differences in soil mass.

    A 2002 study found that six cores per microplot is “adequate” to represent a range of soil samples within more uniform sites: however, this method is not appropriate for all systems (Conant et al., 2002). They recommended that multiple microplots be sampled in the future to decrease variability.

    Conant et al reommended to resample the same microplots for future measurements, as this enhances statistical power and allows changes to be detected years earlier (Conant et al., 2002).

    Sampling from different horizontal strata reduces variability since deeper layers have less spatiotemporal variation and can help to account for differences in soil types, vegetation cover, management, etc. (Donovan, 2013).
    MASS OF CARBON: TOTAL CARBON = FRACTION CARBON (DECIMAL) X DENSITY X VOLUME IN CUBIC METERS
    STANDARD ERROR= STANDARD DEVIATION OF ALL SAMPLES DIVIDED BY SQUARE ROOT OF NUMBER OF SOIL CORES
    Testing microsites to make broad conclusions about a pasture’s soil carbon content is analogous to comparing three tax returns in a small town to gain an accurate view of the average personal income (Donovan, 2013).

    The minimum detectable difference is inversely related to the number of samples required (Conant et al., 2002)>

  • Purpose of our experiment

    The purpose of our experiment is to establish a baseline amount of soil organic carbon in two pastures to compare future measurements to. We chose two pastures that are close in physical proximity but differ in the grazing management applied to them.

  • Hypothesis

    Our hypothesis is that the two pastures have different quantities of soil organic carbon in the 0-10 cm strata due to their different grazing management, but similar quantities in the 10-25 cm and 25-40 cm strata because of their proximity and similar soil types.

  • Description of Cheda Ranch & pastures

    Pasture 1 is located close to a riparian area and borders a barn which was a dairy until the ??. The pasture has a concrete silo for silage storage, and a large carport for storing tractors and machinery. Thus, the pasture has experienced more vehicle traffic than Pasture 2. Pasture 1 was largely left out of the planned grazing and used only when the sheep needed an overflow area for a day or two, so it has been grazed irregularly and overgrazed at times. It is not irrigated.

    Pasture 2 is located on the opposite side of the barn from Pasture 1 and is about __ meters away. It is irrigated regularly during dry summer months, and has been grazed by sheep using holistically planned intensive rotational grazing. It is typically heavily grazed once every 45-50 days and experiences minor, sporadic vehicular traffic.

  • Soil sampling, processing, CN analyzer

    We collected soil samples in early December 2015 using a soil corer to take a 0-10 cm, 10-25 cm, and 25-40 cm sample from stratified simple random sites ?. See fig Donovan's picture for placement of soil samples. The samples were oven-dried and ground with mortar and pestle to homogenize them, then poured through a 2mm sieve to remove rock and root debris. The samples were run through a CN element analyzer make and model.

  • Statistical analysis

  • Don’t need to describe everything…

    • what we tested
    • what was significant in the test
    • significant what did and did not show a difference
  • Credit for stasticians…

    Cover page and acknowledgements page

  • Biological monitoring

    • put in introduction when describing the site
    • put table in Appendice if have data
  • How grazing affects C seq

    Soussana et al conducted a meta-analysis of 115 studies in pastures and grazing land. They found that improved management increased SOC levels in 74% of the studies. Improved management practices included fertilization, grazing management, conversion from cultivation, and improved grass species (Soussana et al., 2010).

    An analysis of 115 studies in pastures found that light grazing increased SOC more than exclosure and heavy grazing (Soussana et al., 2010). However, the article did not specify whether the heavily grazed pastures were on a continuous or rotational grazing system.

    A crucial foundation in any system aiming to increasing SOC retention is to establish ground cover. Permanent soil cover quickly stabilizes water retention and reduces quantities of sediments, nutrients, and agricultural chemicals transported to surface waters within a few years (Whalen et al., 2003).

    EXPERIMENT: A study in the Great Plains chose 3 sites that represented 3 climactic gradients and cultivated native rangelands. In each site, plots were abandoned, seeded with non-native perennial grasses to establish permanent cover, or converted to annual crop production. Samples were obtained from 0-15 cm in depth. The soil bulk density was lower in the undisturbed native rangeland than modified plant communities, and the total C, N, and P contents declined with cultivation. The authors called for a need to collect deeper samples to determine if net gains or losses had occurred throughout the soil profile or were concentrated in the topsoil. The authors found that establishment of perennial grasses or legumes on formerly cultivated land could slow or reverse depletion of SOC, and stabilization or loss of C and N from modified plant communities is affected by climate as well as quantity and chemical characteristics of residues produced by plants (Whalen et al., 2003).

    Little is known about how cattle grazing affects SOC (Pringle et al., 2011).

    The substantial area of the globe devoted to grazing means that minor changes in SOC can cause proportionately large changes in C seq worldwide (Pringle et al, 2011).

    A 2010 global literature review found that SOC changed under contrasted grazing conditions across climactic gradients, and that the factors that control SOC in a grazed ecosystem are more complex than we currently think they are. General patterns that the study noted were that root contents, the primary control of SOC formation, were higher in grazer than ungrazed systems at the most arid and most tropical sites but were lower at temperate sites. The increased root biomass should increase SOC because of greater C inputs to the soils (Pineiro et al., 2010).

    Grazing can change how carbon allocates in the soil. Belowground biomass enters the soil directly and contributes more to soil organic matter formation than aboveground productivity. Grazing changes the proportion of NPP allocated to aboveground or belowground organs (Pineiro et al., 2010).

    One researcher argues that grazing can affect NPP indirectly by altering species composition or soil resources by decreasing water availability (Pineiro et al., 2010).

    “Grazing animals, plants, soil biota and soils have co-evolved for over 20 million years, resulting in highly complex and sensitive inter-relationships” (Jones, 2006).

    A proposed method for how grazing soil carbon is how the plant readjusts for biomass loss after grazing. More carbon is contained in the roots than the leaves of the plant, and when the leaves are removed by grazing, and plant responds by readjusting its biomass balance. Some carbon is mobilized to the crown for production of new leaves, some is lost to the soil as root decomposition, and some is actively exuded into the rhizosphere. Thus, each grazing event becomes a “carbon injection” opportunity (Jones, 2008).

    Plants that are grazed continuously have poorly developed root systems and little C available for exudation into the soil (Jones, 2006).

  • Management recommendations

    Soussana et al made four recommendations in their 2004 study. The authors recommended reducing N fertilizer inputs in highly intensive grasslands, increasing duration of grass fallows, convert fallows to grass-legume mixtures or permanent grasslands, and moderately intensifying nutrient-poor permanent grasslands (Soussana et al., 2004).

    The challenge in determining how management practices affect soil carbon sequestration lies in determining the relationships among precipitation, stocking rate, and carbon dynamics (Fynn et al., 2010).

    Practices that Batjes recommends to enhance soil C seq are to account for different soil types, suitability, and factors for soil formation before cultivating or grazing land. Semi-arid grassland management can focus on reduction of burning, improving the soil nutrient status, and introducing improved grasses and legumes in combination with controlled stocking rates (Batjes 1998).

    More efficient Nitrogen conservation can affect SOC stocks, according to Pineiro et al. The authors recommended avoiding “unwanted” N emissions from excessively loading grazing systems with nitrogen inputs, and that N dynamics would allow increased C seq in soils, and increased soil fertility (Pineiro et al., 2010).

    Dr. Rattan Lal recommends these strategies to increase SOC: soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands (Lal, 2004).

    SOC loss is exaggerated in agricultural ecosystems with severe soil degradation. Carbon loss from soils is emitted directly into the atmosphere and reduces soil quality and biomass productivity, and negatively impacts water quality (Lal, 2004).

    Management practices that are recommended by Lal add biomass to the soil, cause minimal soil disturbance, improve soil structure, enhance soil microbiota biodiversity, and strengthen mechanisms of nutrient and water cycling (Lal, 2004).

    “Long term enhancement of SOC seq requires sustained primary productivity and efficient feedback between communities of plants and soil biota for carbon and nutrient cycling” (De Deyn et al., 2008).

    Maximizing the balance between soil carbon input and output is the best way to enhance SOC seq (De Deyn et al., 2008).

    Changing management practices to those that shift the soil biochemical environment to favor fungi can reduce the rates of SOC decomposition and enhance sequestration. Practices that show potential for accomplishing this include planting perennial species, reducing tillage, maintaining neutral soil pH, ensuring adequate drainage, and minimizing erosion (Jastrow et al., 2007).

    Management recommendations made by Flynn et al for increased carbon sequestration include adjustments in stocking rates, introduction of grasses on degraded lands, managing invasive species, reseeding grassland species, riparian zone restoration, and introduction of biochar to soils (Fynn et al., 2010).

  • Carbon Markets

    Carbon markets have been in use since 2002, mostly in European Union countries. The “commodification of soil C is important for trading C credits” (Lal, 2004).

    The basic idea of a “carbon market” is to instill a financial incentive to producers to sequester soil organic carbon on their land. Increased soil carbon levels would be converted to verified emissions reductions to use within an offset market, cap and trade system, or other credit program (Fynn et al., 2010).

    In terms of sampling, accuracy costs more and cheaper methods are traditionally less accurate (Fynn et al., 2010).

    “Rather than tie a protocol to the limitations of one particular method, it is logical to combine the strengths of different methods into a single methodology, which may be updated as economics and technical advances allow” (fynn et al., 2010).

    #Lara et al., nd
    Quantifying “ecosystem services” is a complex and convoluted process, albeit necessary to quantify the value to human societies that natural capital resources bring. Modern agriculture is a “major driver of global environment change” and there are numerous efforts to establish sophisticated economic models to predict global effects of carbon sequestration efforts. These include ARIES (artificial intelligence for ecosystem services) which takes open source data into account, InVEST (integrated valuation of ecosystem services and tradeoffs) which provides maps of monetary value among other outputs, and MAgPIE (Model of agricultural production and its impact on the environment) which shows potential output of carbon storage in soils and crop residue, etc (Lara et al, nd). These are just a few of numerous modeling systems that could be of future use towards establishing a global or domestic carbon market.

  • Conclusion

    “The role of agriculture in sequestering of organic C by soils remains ambiguous. The overall picture is complicated by technological, social, economical and cultural factors” (Batjes 1998).

    Carbon sequestration is a bridge between 3 global issues: climate change, desertification, and biodiversity (Lal, 2004). Regardless of the climate change debate, it is a crucial issue that could increase productivity and water quality and restore degraded ecosystems (Lal, 2004).

    Agriculturally developing nations, especially those in tropical climates where dynamic soil processes exacerbate rates of SOC accumulation or loss, have the greatest need for change. Currently, the C sink capacity is high, but the rate of C seq is low and complicated by limited infrastructure and resource-poor agricultural systems (Lal, 2004).

    Generally, soil C seq by adapting recommended management practices is a natural, cost-effective, and environmentally-friendly process (Lal, 2004).

    The scientific community needs to be open to new plant traits and pathways of carbon flow, as we discover more about soil microbiota and their ecosystems (De Deyn et al., 2008).

  • #Bland 2015

    The Lima-Paris Action Agenda, unveiled at the United Nation Climate Change Conference in November 2015, announced that the carbon farming movement is “moving forwards”. Targeting the Action Agenda’s goal of resilient societies with low carbon levels, it stated that a “growing” number of advocates say that “one of the best opportunities for drawing carbon back to Earth is for its land managers to sequester more carbon in the soil” (Bland, 2015).
    #Ministry of Ag, 2015

    In December 2015, France unveiled its new 4% Initiative, which is a voluntary group of stakeholders committed to action plans that implement management practices to enhance the soil organic pool of France’s soils. The initiative’s plan of action included structuring for multipartner action programs to better manage for soil carbon, and funding for international research and scientific cooperation programs. The plan’s title comes from a powerful hypothesis that a 4% annual growth rate of soil organic carbon stock would stop the present increase in atmospheric CO2.
    #Porter et al, 2014

    The response of pastures to climate change is complex because it is riddled with indirect interactions of plant, soil, and atmospheric interactions at the biogeochemical level (Porter et al., 2014).

    Increasing vegetative cover reduces soil erosion and loss of nutrients, increases soil carbon and resists temperature extremes (Porter at al., 2014).

  • California annual grasslands differ from their Midwestern counterparts, perennial temperate grasslands. California is characterized by wet winters and dry summer, with grasslands dominated by annual grasses and forbs which die during dry, warm summer months and create thick surface litter (Silver et al., 2010).

    California annual grasslands experience a period of annual grass death during dry, warm summer months, which creates a generally shorter root system than perennial grasslands. This is speculated to lead to lower soil C sequestration rates relative to perennial grasslands (Silver et al., 2010).

    Grazing management traditionally utilized in annual grasslands extrapolates a delicate balance between residual dry matter and the following year’s productivity (Silver et al., 2010).

    Soil carbon analyses performed on a regional scale are an effective way to trace the sensitivity of soil carbo pools to the environment and management practices. These analyses should include information on climatic patterns, soil type, cover type, and management (Silver et al., 2010).

    A review of soil analyses in California annual grasslands found a wide range of soil carbon across similar soil types and climate, suggesting “considerable potential” to increase soil carbon sequestration through changing management (Silver et al., 2010).

    • Climate Change impact statement

      In the next century, the world faces a 2 degree C or greater air temperature increase (Waltman et al., 2010). Climate change is an all-encompassing global problem that threatens food security, water availability, civil unrest, and more. The agricultural sector has significant opportunities to mitigate GHG emissions, and currently one substantiated option is to increase carbon sequestration (Waltman et al., 2010).

      The International Panel on Climate Change predicts that the global energy supply will continue to be dominated by fossil fuels until at least 2050 (IPCC, 2005). That means that an alternative to mitigating GHG emissions must lie in another sector. Enteric fermentation and agricultural soils contribute to 76% of total agricultural emissions, while biomass burnings account for 6-12%, and synthetic fertilization for 12% (Smith et al., 2014). Carbon sequestration is hailed as the win-win situation for producers, land managers, environmentalists, and climate-change advocates. The Lima-Paris Action Agenda, unveiled at the United Nation Climate Change Conference in November 2015, called carbon sequestration “one of the best opportunities for drawing carbon back to Earth” (Bland, 2015). With the obvious necessity to make changes to the agricultural sector to avoid the catastrophic effects of climate change, it is pertinent to examine the effects of agricultural management practices on carbon sequestration.

    • Definition

      The Department of Energy defines carbon sequestration as “the provision of long-term storage of carbon in the terrestrial biosphere, underground, or in the oceans so that the buildup of CO2 will reduce or slow.” (Lal, 2007). Simply put, it is the act of transferring atmospheric CO2 into pools elsewhere in the biosphere and storing it in a way that it is not immediately reemitted (Lal, 2004). “Carbon sequestration” can also refer to the act of increasing the SOC pool through changing land management practices (Lal, 2004). In terms of soil, sequestration refers to the abilities of soil to store atmospheric carbon in the soil as humified organic carbon (Jones, 2008).

      Sequestration can be natural or anthropogenic-driven. Anthropogenic sequestration methods include geological storage, ocean storage, and industrial fixation of CO2 in inorganic carbonates (IPCC, 2005). Natural sequestration is limited to soils and trees (Lal et al., 2007).

    • History

      Carbon sequestration was first brought into the climate change spotlight in the 1970s, when a study proposed that planting trees could offset carbon emissions (Ellert et al., 2002). Since then, the idea of carbon sequestration has been evolved and refined to management-driven predictions of how manipulating the soil organic carbon pools can change CO2 levels in the atmosphere.

    • Implications

      Soil carbon storage is a key component of the global carbon cycle (De Deyn et al., 2008). By manipulating the carbon cycle to draw more carbon into the soil than is taken out of it, more and more research is showing abilities of management practices to mitigate climate change. Carbon sequestration is becoming a global issue with many contexts and uses throughout industries (Donovan, 2013).

      The estimated range of carbon sequestration that could potentially offset fossil fuel emissions varies widely in scientific literature, and seems largely dependent on what modeling technology is used. Dr. Rattan Lal estimates that with proper management changes, 0.4-1.2 Gt C/yr, or 5-15% of global fossil fuel emissions, can be sequestered (Lal, 2004). Each ton of stored carbon in soils removes 3.67 tons of CO2 from the atmosphere (Fynn et al., 2010).

      The global soil organic carbon pool is 3.3 times the size of the atmospheric carbon pool, and 4.5 times the size of the biotic pool (Lal, 2004). Most global soils contain anywhere from 50-150 tons per hectare of carbon in the upper 100 cm (Lal, 2004). The potential for carbon sequestration, while finite, seems to be astonishingly large for the amount of controversy surrounding it. Agricultural soils have lost an estimated 50 Gt of carbon (Soussana et al., 2010), largely through practices that erode or degrade soils. Modeling technology can help a great deal with predicting how global soils will change, but smaller, direct-measurement studies are needed to firmly establish trends in SOC pools.

    • Why grasslands

      Grasslands cover a quarter of the earth’s surface, are found on every continent, and contribute to the livelihoods of 800 million people (Soussana et al., 2010). They might well be the biome that is the most intimately associated with human life and productivity. Livestock uses 3.4 billion hectares of grazing land, and a quarter of global crop land is dedicated to growing livestock feed (Soussana et al., 2010). Grazed grasslands are generally under close human management, which gives a single producer the unique ability to manipulate a variety of traits on their land that could potentially affect carbon sequestration. Grazing lands contain 10-30% of the world’s soil organic carbon (Whalen et al., 2003).

      Grasslands are a major focus of carbon sequestration research because they are typically rich in soil organic carbon. Grassland soils have soil characteristics that promote aggregate formation that microorganisms form into micro-aggregates, the form in which soil organic carbon stabilizes the longest (Soussana et al., 2010). Soil organic matter, a major determinant of the dark-colored soils and mollisols associated with grasslands, also determines soil fertility, water retention, and soil structure (Pineiro et al., 2010).

      The soil organic carbon sequestration potential for cropland and grazing land in the United States is 180 Mt SOC/yr (Lal et al., 2007). A small change in soil organic carbon could have a large impact on overall emission reduction, due to the large surface area represented by rangelands (Fynn et al., 2010).

    • Our grassland

    • Forms of carbon in soil

      Typically, soil organic carbon is measured in the top soil and in organic form. While carbon can be sequestered as secondary carbonates, the rate is low (Lal, 2004). Most accumulation happens in the 0-30 cm soil strata, although slow accumulation and rapid loss can occur from deeper horizons (Soussana et al., 2010). Carbon is usually not measured in vegetation, because net primary productivity is either transferred to animals via grazing, taken from the land as crops, or returned to the soil as litter.

      There are 3 forms of carbon in soil. The largest fraction is organic soil carbon, which is derived from living tissue. It is critical in the formation of soil aggregates but is typically the least stable form of carbon. Charcoal is derived from living tissue as well, so is considered organic and is also more resistant to decomposition. Inorganic soil carbon is the most stable form because it is protected from decomposition but typically changes at a slower rate (Donovan, 2013).

    • Nonlinear acquisition of C

      Modeling suggests that soil organic carbon accumulates over time in a non-linear manner. Lal proposes it follows a sigmoid curve, reaches the maximum sequestration rate 5-20 years after management changes and then falls into an equilibrium rate (Lal 2004). Climate has a large effect on the rate of sequestration- dry and warm regions have slower rates, upwards of 150 kG/ha/yr, while humid and cool climates could have rates up to 1000 kg/C/ha/yr (Lal 2004). One study estimates the time to reach equilibrium at up to 50 years after each disturbance (Batjes 1998). Simply put: after a change in management or some other disturbance alters soil organic carbon pool, a new rate of sequestration (or emission) is set in motion and continues at the new kinetic rate until an equilibrium is reached, at which time the rate of sequestration/emission levels off and remains constant until the soil organic carbon pool “capacity” is reached. The rate is changed each time a new disturbance takes place, which is why it is crucial to keep management practices steady- new word while the new rate is setting pace for sequestration.

    • Protecting from decomposition

      Organic carbon can remain in soils for hundreds of years if left undisturbed, and carbon dating placed substantial amounts of soil organic carbon in deeper layers of soil several millenia ago (Soussana et al., 2010). However, soil organic carbon that is not stabilized in soil is quickly emitted back into the atmosphere through microbial respiration and decomposition. The two major ways that SOC is stabilized in soil, that we have so far discovered, it through biochemical and physical protection. Biochemical alteration is the process of transforming SOC to chemical forms that are resistant to decomposition (Jastrow et al., 2007). Positively charged SOC molecules are chemically bonded to negatively charged iron and clay anions (Fynn et al., 2010). Physical protection is the process by which biochemical “glues” like glomalin hold soil aggregates together (Fynn et al., 2010). In order words, SOC is occluded within aggregates, sequestered deep within tiny pores inaccessible to microbial decomposers (Jastrow et al., 2007).

    • How long C stays in soil

      Soil organic carbon can be easily lost back into the atmosphere if it is not properly protected from microbial decomposition (Soussana et al., 2010). SOC in deeper soils is farther from the major microbial communities and energy that decomposes surface organic matter (Soussana et al., 2010), which contributes to its relatively low rates of flux throughout time.

      Different research suggests different mean residence times for soil organic carbon, and the type of carbon that is studied must be examined for accurate comparison. Fynn et al suggests that there are two types of carbon accumulated, each with different mean residence times. He terms the “light fraction”, which is made of fresh plant materials that are rapidly decomposed and turn over within a few years. The “heavily occluded” fraction is composed of carbohydrates and humic materials that can remain in soils for indefinite periods of time, pending that the soil remains undisturbed. The light fraction seems to be what changes spatiotemporally, and will change the most readily in response to management changes (Fynn et al., 2010).

    • Models & their Variabilities

      Models that attempt to predict the rates and amounts of carbon that agricultural land can sequester are incredibly useful, and simultaneously flawed beyond useful accuracy. A 2004 French study utilized several modeling systems to demonstrate variabilities in a large database collected in 2002. The 19,000 unpublished references and 1000 literature references examined data taken from the upper 30 cm of soil and attempted to quantify fluxes in SOC stock and GHG changes to generalize conclusions regarding the kinetics of SOC accumulation (Soussana et al., 2004). The great benefit of conceptual models is the ability to collect and analyze huge amounts of data at one time, which will prove to be an invaluable tool when producers are looking to make changes on large tracts of land.

      However, quantifying the relationships between SOC pools and the related variables is challenging and convoluted. Storage of SOC is typically determined by the amount of net primary production that is allocated to belowground plant roots, while factoring in the effects of climate, biota, time, topography, and parent materials (Pineiro et al., 2010). The conceptual models estimate that changes in SOC stocks are determined by the balance between C and N inputs and outputs, respiration, and plant production- seen as carbon outputs (Pineiro et al., 2010). The models assume that abiotic and management-driven factors operate via cascade effects through shorter-term controls (Pineiro et al., 2010).

      These conventional models assume that the only carbon input in soils comes from biomass inputs from decomposition of surface litter and belowground roots (Jones, 2008). In other words, the models only consider the light fraction of carbon made of decomposing plant materials (Fynn et al., 2010), which is why most experimental models conclude high spatiotemporal variability and low rates of carbon sequestration that is easily released back into the atmosphere.

    • Spatiotemporal variability

      The use of modeling to determine SOC sequestration capacity is in part limited by the inherent spatial variability in soils that limits the precision of measurements (Conant et al., 2002). Spatial variation is compounded by soil variation, microclimate, fire history, topography, and plant communities (Pringle et al., 2011). Soil carbon stocks in grasslands have higher spatial variability than crop land (Soussana et al., 2004), and forested areas have greater spatial variability than cultivated sites (Conant et al., 2002). It is difficult to distinguish between natural fluxes in carbon stocks due to the factors described above, and changes that are driven by land management. However, several statistical analyses have found that small changes in SOC are detectable with the proper controlled measurement (Conant et al., 2002). Donovan recommends waiting longer between samplings, at least a few years, to maximize the chance of detecting actual change, and distinguish between year-to-year variability (Donovan, 2013).

    • Mycorrhizae and humification

      A glaring error in early carbon sequestration research is the absence of the role of mycorrhizal fungi and humification in storing organic carbon. Mycorrhizal fungi is still relatively poorly understood, as they are exceedingly fragile, can take several years to establish, and are destroyed in seconds following herbicide application and physical disturbance like tilling (Allen, 2006). In addition, although the fungi networks can constitute 20-30% of the total soil microbial biomass, they are not detected by standard biomass sampling techniques and have remained fully undiscovered (Leake eta l., 2004). However, there can be several kilometers of hyphae present in a single gram of soil (Allen, 2006) and the structural complexity of mycelial networks is only recently discovered (Leake et al., 2004).

      Considered by some to be the most dynamic and diverse component of symbiosis (Leake et al., 2004), the simple role of myocorrhizal fungi is to transport nutrients to the plant in exchange for carbon in the form of sugars (Jones, 2008). Generally stated, the hyphae carry carbohydrates from plants into soil regions far beyond the typical rhizosphere, and release exudates and other compounds to interact with deep soil microbiota (Leake et al., 2004).

      There is a crucial link between mycorrhizal hyphae exudates and carbon sequestration that has been largely overlooked by conventional modeling. Christine Jones has coined the term, “liquid carbon pathway” to describe the abilities of mycorrhizal hyphae to carry carbon deep into the soil, where it is humified into stable form that can remain there for hundreds of years (Jones, 2008). Arbuscular mycorrhizal fungi, conventionally considered as agriculturally important to soil fertility (Jones, 2008), secretes glomalin that accumulates in soil and contributes to a substantial proportion of stable SOC (Leake et al., 2004). Humic substances were once thought to be huge polymers, but now are suggested as being associations of small molecules held by weak forces that interact with organic compounds in soils (Spaccini et al., 2002). Humification is a process that requires mycorrhizal fungi, nitrogen fixing bacteria, and phosphorus solubilizing bacteria (Jones, 2008). Carbon that is sequestered into the humic pool is protected from microbial degradation by the biochemical means described early in this article (Spaccini et al., 2002). The most impactful part of this relationship may be the proposal that humified soil organic carbon has an average residence time in soil of several hundreds of years (Spaccini et al., 2002).

      Conventional models of soil organic carbon sequestration rest upon the assumption that the only carbon inputs to soil are root decomposition, sloughed cells, (Leake et al., 2004) and surface decomposition provide the only significant carbon inputs to soils. However, up to 15% of the SOC stock can be contributed by mycorrhizal fungi (Leake et al., 2004)- and that’s only based on the recent discoveries of hyphae networks whose relationships are not yet fully understood. The humified carbon that can form deep in the soil profile may prove the unseen savior of carbon sequestration as a valid climate change mitigator (Jones, 2008).

    • Direct measurement

      SOC sequestration can be estimated by directly measuring changes in carbon pools or indirectly by measuring carbon fluxes (Soussana et al., 2010). Donovan lists 5 laboratory techniques to measure soil carbon directly from soil samples. These include elemental analysis by dry combustion, acid treatments, loss on ignition, carbon fractions, and soil respiration. Of these, elemental analysis by dry combustion is considered the most accurate that is likely to detect change in the organic carbon fraction but measures total soil carbon (inorganic and organic) (Donovan, 2013). Since large quantities of carbon are already present in the soil, sensitive methods are needed to detect small changes (Ellert et al., 2002). Most SOC studies focus on the 0-30 cm soil strata (Soussana et al., 2010) because of the traditional thought that sequestration is brought about from decomposing surface litter and roots.

    • Sample size

      Cost and practicality are limiting factors when taking soil measurements, and for the purposes of this experiment we were limited to very few samples (XX in total). However, Pringle et al found success with taking 25 soil samples per unit to estimate baseline mean soil organic carbon to within 20% of the true mean to a depth of 30 cm (Pringle et al., 2011). A 2002 study found that six cores per microplot is adequate to represent a range of soil samples within more uniform sites, however this strategy is limited to systems with more inherent spatiotemporal variability (Conant et al., 2002). Multiple microplots should be sampled to decrease variability (Conant et al., 2002).

      Sampling from different horizontal strata reduces variability since deeper layers have less spatiotemporal variation and can help to account for differences in soil types, vegetation cover, and management (Donovan, 2013). The power of testing microsites to make broad generalizations about an entire pasture is limited (Donovan, 2013), and taking samples from multiple microplots in the future will decrease variability (Conant et al., 2002).

      The purpose of our experiment was to establish a baseline SOC pool in two separate pastures to compare future carbon changes, if any. The same microplots will be samples in the future to enhance statistical power (Conant et al., 2002).

      • Get GPS coordinates
        *Quantify high-intensity short-duration grazing — stocking density, duration of grazing, rest period
      • get ahold of Donovan
      • CN element analyzer make & model- or as footnote
      • soils that comprise majority of pasture
      • taxonomic description
      • depth of soil & of different horizons
      • soil texture
      • bulk density
    • #Results

      Experimental Results

      We looked at three comparing three variables analyzed during this experiment: comparison between pastures, strata, and pasture by strata. We used an alpha of 0.05 to detect small changes, and found no significant difference between the pastures (p=0.865), and no significant difference between pasture by strata (p=0.114). We found a significant difference between strata (p=0.000) as was expected due to the large amount of soil organic matter residing in the topsoil. The mean of the 0-10 cm, 10-25 cm, and 25-40 cm layer were significantly different from each other (3.07875, 1.88863, and 1.42988 respectively). We completed a power curve for general full factorial, and found that with 8 samples taken from the 0-10 cm layer, we had close to 100% power of detecting a 0.4 percent change in carbon. This is especially useful to land managers who wish to implement a small-scale carbon monitoring program without inputting costly equipment and labor to take research-scale sample sizes.

    • Small changes in carbon pools have drastic effects in the global climate system (Schlesinger, 1995).
      Losses in soil organic matter can exacerbate global warming, but increases in soil organic matter can slow the rate of atmospheric CO2 release and “provide a negative feedback” to global warming (Schlesinger, 1995).

    • Grazing affects on SOC seq

      The impact that soil carbon sequestration might have on global soils is effectively useless if the rates of sequestration or emissions cannot be manipulated by human management. For the purposes of this experiment, we are focusing on grazing land. The substantial area of the globe utilized for grazing means that small changes in SOC can cause proportionately large changes in global carbon sequestration (Pringle et al., 2011). However, little is currently known about how cattle grazing affects SOC (Pringle et al., 2011).

      A 2010 global literature review found that SOC changed under contrasted grazing conditions across climactic gradients, and that the factors that control SOC in a grazed ecosystem are more complex than we currently think they are. General patterns that the study noted were that root contents, the primary control of SOC formation, were higher in grazer than ungrazed systems at the most arid and most tropical sites but were lower at temperate sites. The increased root biomass should increase SOC because of greater C inputs to the soils (Pineiro et al., 2010). An analysis of 115 studies in pastures found that light grazing increased SOC more than exclosure and heavy grazing (Soussana et al., 2010). However, the article did not specify whether the heavily grazed pastures were on a continuous or rotational grazing system. One researcher argues that grazing can affect NPP indirectly by altering species composition or soil resources by decreasing water availability (Pineiro et al., 2010). Studies have found that SOC increases, decreases, or is relatively maintained in different grazing systems across climatic gradients, and the future question will be to describe exactly how grazing management manipulates the rate of carbon sequestration.

      Grazing is inherently difficult to describe in an experimental system because of the many different ways to graze pastures, the type of pasture that is being grazing, and abiotic climatic factors that affect the way grazing is conducted, as well as the different animals that graze in different ways and hence exert different affects on the aboveground and belowground communities. Christine Jones writes elegantly, “Grazing animals, plants, soil biota and soils have co-evolved for over 20 million years, resulting in highly complex and sensitive inter-relationships” (Jones, 2006). There is no universal way to describe how grazing affects soil carbon sequestration, but the attempts are to broadly describe affects that should either entice or discourage producers from making changes that could enhance or stop soil carbon sequestration.

      One very simple proposed method for how grazing soil carbon is how the plant readjusts for biomass loss after grazing. More carbon is contained in the roots than the leaves of the plant, and when the leaves are removed by grazing, and plant responds by readjusting its biomass balance. Some carbon is mobilized to the crown for production of new leaves, some is lost to the soil as root decomposition, and some is actively exuded into the rhizosphere. Thus, each grazing event becomes a “carbon injection” opportunity (Jones, 2008). However, much more research is indicated to examine different grazing management systems and their affects on soil microbial communities such as arbuscular mycorrhizal fungi, that will in turn affect rates of carbon sequestration. In addition, the best way to compile data on different management systems is to educate and encourage producers to start their own carbon monitoring practices that can be compiled into open-source data networks, much like the Soil Carbon Coalition, a non-profit organization dedicated to sharing open-source data between producers (Donovan, 2015).

      We propose that in the ensuing five years, the amount of carbon contained in our pastures will change based on the grazing management applied to the pastures. In December 2015, both pastures were seeded with a no-till seeded with a cover crop cocktail of ??. The drylot pasture was incorporated into the grazing plan and will experience the same short-duration, high-intensity rotational grazing that the irrigated pasture is managed with, but with a smaller duration of time. We hypothesize that in five years, the carbon content of the drylot pasture will have increased in the A strata, and will likely increase in the B and C layer due to better-developed root systems that can partner with mycorrhizal fungi to channel carbon deeper into the soil profile. If grazing management, irrigation management, and soil disturbances are well managed, there should be an increase of carbon in the irrigated pasture as well. If management stays approximately the same, the carbon content in the irrigated pasture should reflect only natural fluxes.

    • Management Recommendations

      Recent studies have suggested that making changes in land management, some minor and some drastic, can improve the rates of soil carbon sequestration. Soussana et al conducted a meta-analysis of 115 studies in pastures and grazing land. They found that improved management increased SOC levels in 74% of the studies. Improved management practices included fertilization, grazing management, conversion from cultivation, and improved grass species (Soussana et al., 2010). The challenge in determining how management practices affect soil carbon sequestration lies in teasing apart the relationships between climate, stocking rates, grazing systems, and carbon dynamics (Fynn et al., 2010). Some broadly drawn recommendations have been made, most stemming from factors that have been solidly shown to improve factors that lead to improve soil carbon sequestration. In semi-arid grasslands, producers should reduce burning, control stocking rates, and improve nitrogen dynamics by avoiding excessive nitrogen inputs (Batjes 1998, Pineiro et al., 2010).

      Changing management practices to those that shift the soil biochemical environment to favor fungi can reduce the rates of SOC decomposition and enhance sequestration. Practices that show potential for accomplishing this include planting perennial species, reducing tillage, maintaining neutral soil pH, ensuring adequate drainage, and minimizing erosion (Jastrow et al., 2007).

      General grazing system management changes emerging in the realm of sustainability research show promise to improve soil carbon sequestration as well. These include adjustments in stocking rates, introduction of grasses on degraded lands, managing invasive species, reseeding grassland species, riparian zone restoration, and introduction of biochar to soils (Fynn et al., 2010).

      An indirect way to improve soil carbon sequestration is to avoid the loss of soil organic carbon through soil disturbance. SOC loss is exaggerated in agricultural ecosystems with severe soil degradation. Carbon loss from soils is emitted directly into the atmosphere and reduces soil quality and biomass productivity, and negatively impacts water quality (Lal, 2004).

    • Carbon markets

      Carbon markets are an economically crucial conversation to have whenever discussing soil carbon sequestrations. The basic idea of a “carbon market” is to instill a financial incentive to producers to sequester soil organic carbon on their land. Increased soil carbon levels would be converted to verified emissions reductions to use within an offset market, cap and trade system, or other credit program (Fynn et al., 2010). Carbon markets have been in use since 2002, mostly in European Union countries (Lal, 2004). Quantifying “ecosystem services” is a complex and convoluted process, albeit necessary to quantify the value to human societies that natural capital resources bring (Lara et al., nd). There have already been numerous efforts to establish economic models to predict global effects of carbon sequestration efforts (Lara et al., nd). While these are largely out of the scope of this paper, it is important that to mention that the more we know about the relationships of carbon sequestration and grazing practices, the closer we can get to establishing carbon markets that provide incentive to producers to make changes that will simultaneously mitigate climate change.

    • Conclusion

      The purpose of this research was to test an economically viable, low-labor method to establish a baseline soil organic carbon pool to make future comparisons to in five years. We found that there were significant differences in SOC content between two pastures that are in close proximity but have been under differing grazing management, and that our soil sample number [ ] ?? gave sufficient confidence to detect changes in years to come. This is encouraging to land managers and producers who wish to establish their own carbon monitoring systems without the use of much funding or infrastructure in preparation for the establishment of a formal carbon market. More research is indicated to establish the increments of accuracy that are found at greater numbers of microsites tested, and increased core samples within microsites.

      There has been an increase in focus on carbon sequestration. In December 2015, France unveiled its 4% Initiative, which is is a voluntary group of stakeholders committed to action plans that implement management practices to enhance the soil organic pool of France’s soils. The initiative’s plan of action included structuring for multipartner action programs to better manage for soil carbon, and funding for international research and scientific cooperation programs (Ministry of Agriculture, 2015). Generally, the recommended management practices to improve soil carbon are natural, cost-effective, and environmentally-friendly (Lal, 2004). While more governments and agricultural programs are becoming open to the idea of carbon sequestration as a viable way to restore degraded agricultural lands, more research is called for to better understand the relationships between agricultural systems and carbon dynamics. The scientific community needs to be open to new pathways of carbon flow, as we discover more about soil microbiota and their ecosystems (De Deyn et al., 2008). Producers should begin to implement their own carbon monitoring methods, both in preparation for impending carbon market systems and in tandem with soil improvement strategies. The research techniques delineated in Donovan’s “Measuring Soil Change” are low-cost strategies that producers can use with their own equipment and very little money to analyze soil carbon content with statistical validity. Open-source data from individual producers could aid greatly in understanding the relationships between management changes and soil carbon pools, as there is a lack of published data from California in particular, namely in areas that are not in close proximity to agricultural research stations (Silver et al., 2010). There should be further research in establishing economically viable and statistically significant techniques to link land management to changes in soil carbon pools to better understand the effect of soil health on carbon sequestration, and carbon sequestration on soil health.

    • #UNLPAA 2015

      Press release from Lima-Paris Action Agenda

      The Lima-Paris Action Agenda, a joint undertaking of Peruvian and French presidencies, the Office of the Secretary-General of the UN and the UNFCCC Secretariat, met in December 2015 to cement action plans to tackle the global issue of climate change. They focused in on 6 major initiatives that support farmers, including France’s 4% Initiative; Live Beef Carbon, a European cooperative to reduce the carbon footprint of the livestock sector; Adaptation for Smallholder Ag Program, investing climate finance for developing countries; and the Agro-ecology funding for West African countries, among more (UN LPAA, 2015).

    • #Introduction

      Introduction to carbon sequestration and grassland implications

      In the next century, the world faces a 2 degree C or greater air temperature increase (Waltman et al., 2010). Climate change threatens food security, water availability, civil unrest, and more (Lal, 2004). The agricultural sector has significant opportunities to mitigate greenhouse gas (GHG) emissions, and currently one substantiated option is to increase carbon sequestration (Waltman et al., 2010).

      The International Panel on Climate Change predicts that the global energy supply will continue to be dominated by fossil fuels until at least 2050 (IPCC, 2005). An alternative to mitigating GHG emissions must be found by other means. Enteric fermentation and agricultural soils contribute to 76% of total agricultural emissions, while biomass burnings account for 6-12%, and synthetic fertilization for 12% (Smith et al., 2014). Carbon sequestration is regarded as a positive strategy for producers, land managers, environmentalists, and climate-change advocates. The Lima-Paris Action Agenda, unveiled at the United Nation Climate Change Conference in November 2015, called carbon sequestration “one of the best opportunities for drawing carbon back to Earth” (Bland, 2015). With the obvious necessity to make changes to the agricultural sector to avoid the catastrophic effects of climate change, it is pertinent to examine the effects of agricultural management practices on carbon sequestration.

      The Department of Energy defines carbon sequestration as “the provision of long-term storage of carbon in the terrestrial biosphere, underground, or in the oceans so that the buildup of CO2 will reduce or slow.” (Lal, 2007). Simply put, it is the act of transferring atmospheric CO2 into pools elsewhere in the biosphere and storing it in a way that it is not immediately reemitted (Lal, 2004). Carbon sequestration can also refer to the act of increasing the SOC pool through changing land management practices (Lal, 2004). Sequestration can be natural or anthropogenic-driven. Anthropogenic sequestration methods include geological storage, ocean storage, and industrial fixation of CO2 in inorganic carbonates (IPCC, 2005). Natural sequestration is limited to soils and trees (Lal et al., 2007). Carbon sequestration was originally pulled into the climate change spotlight in the 1970s, when a study proposed that planting trees could offset carbon emissions (Ellert et al., 2002). Since then, we have discovered that the soil biome has unprecedented potential to capture carbon. Soil has tremendous ability to pull in carbon from the atmosphere and store it in soil as humified organic carbon (Jones, 2008).

      Soil carbon storage is a key component of the global carbon cycle (De Deyn et al., 2008). It is critical that we can quantify the ability of management changes to manipulate the carbon cycle to pull more carbon into the soil than is taken out of it. The estimated range of carbon sequestration that could potentially offset fossil fuel emissions varies widely in scientific literature, and seems largely dependent on what modeling technology is used. On the upper end, Lal estimates that with proper management changes, 0.4-1.2 Gt C/yr, or 5-15% of global fossil fuel emissions, can be sequestered (Lal, 2004). Each ton of stored carbon in soils removes 3.67 tons of CO2 from the atmosphere (Fynn et al., 2010).
      The global soil organic carbon pool is 3.3 times the size of the atmospheric carbon pool, and 4.5 times the size of the biotic pool (Lal, 2004). Most global soils contain anywhere from 50-150 tons per hectare of carbon in the upper 100 cm (Lal, 2004). The potential for carbon sequestration, while finite, seems to be astonishingly large. Agricultural soils have lost an estimated 50 Gt of carbon (Soussana et al., 2010), largely through practices that erode or degrade soils. Modeling technology can help a great deal with predicting how global soils can change, but smaller, direct-measurement studies are needed to firmly establish trends in SOC pools.

      In this study, we compared two pastures on a sheep grazing ranch at California Polytechnic State University San Luis Obispo. The pastures are characteristic of California’s annual grasslands. Grasslands cover a quarter of the earth’s surface and contribute to the livelihoods of 800 million people (Soussana et al., 2010). They might well be the biome that is the most intimately associated with human life and productivity. Livestock uses 3.4 billion hectares of grazing land, and a quarter of global crop land is dedicated to growing livestock feed (Soussana et al., 2010). Grazed grasslands are generally under human management, which gives a the land owner or manager the unique ability to manipulate a variety of traits on their land that could potentially affect carbon sequestration. Grazing lands contain 10-30% of the world’s soil organic carbon (Whalen et al., 2003) and are a major focus of carbon sequestration research because they are typically rich in soil organic carbon. Grassland soils have soil characteristics that promote aggregate formation that microorganisms form into micro-aggregates, the form in which soil organic carbon stabilizes the longest (Soussana et al., 2010). Soil organic matter, a major determinant of the dark-colored soils and mollisols associated with grasslands, also determines soil fertility, water retention, and soil structure (Pineiro et al., 2010).
      The soil organic carbon sequestration potential for cropland and grazing land in the United States is estimated to be 180 Mt SOC/yr (Lal et al., 2007). A small change in soil organic carbon could have a large impact on overall emission reduction, due to the large surface area represented by rangelands (Fynn et al., 2010). There is a large potential for research to quantify management practices that can improve soil carbon sequestration on grasslands, and the variable that we are manipulating is low-input grazing management. We hypothesize that by manipulating the stocking density, intensity and duration of grazing, irrigation management, and soil disturbances, we will see an increase in soil carbon pools in five years.

    • #Introduction

      Carbon sequestration biomechanics

      Typically, soil organic carbon is measured in the top soil and in organic form. While carbon can be sequestered as secondary carbonates, the rate is low (Lal, 2004). Most accumulation happens in 0-30 cm soil depth, although slow accumulation and rapid loss can occur from deeper horizons (Soussana et al., 2010). Carbon is usually not measured in vegetation, because net primary productivity is either transferred to animals via grazing, taken from the land as crops, or returned to the soil as litter.
      There are 3 forms of carbon in soil. The largest fraction is organic soil carbon, which is derived from living tissue. It is critical in the formation of soil aggregates but is typically the least stable form of carbon. Charcoal is derived from living tissue as well, so is considered organic and is also more resistant to decomposition. Inorganic soil carbon is the most stable form because it is protected from decomposition but typically changes at a slower rate (Donovan, 2013).

      Organic carbon can remain in soils for hundreds of years if left undisturbed, and carbon dating placed substantial amounts of soil organic carbon in deeper layers of soil several millenia ago (Soussana et al., 2010). However, soil organic carbon that is not stabilized in soil is quickly emitted back into the atmosphere through microbial respiration and decomposition. The two fundamental ways that SOC is stabilized in soil, that we have so far discovered, it through biochemical and physical protection. Biochemical alteration is the process of transforming SOC to chemical forms that are resistant to decomposition (Jastrow et al., 2007). Positively charged SOC molecules are chemically bonded to negatively charged iron and clay anions (Fynn et al., 2010). Physical protection is the process by which biochemical “glues” like glomalin hold soil aggregates together (Fynn et al., 2010). In order words, SOC is occluded within aggregates, sequestered deep within tiny pores inaccessible to microbial decomposers (Jastrow et al., 2007).

      If soil organic carbon is not protected, it is easily lost back into the atmosphere (Sousanna et al., 2010). Disturbances are a major source of carbon loss, and thus soil organic carbon pools deeper in the soil are farther from the microbial ecosystems that decompose surface organic matter (Soussana et al., 2010) which contributes to its low rates of flux over time.

      Different research suggests different mean residence times for soil organic carbon, and the type of carbon that is studied must be examined for accurate comparison. Fynn et al suggests that there are two types of carbon accumulated, each with different mean residence times. He terms the “light fraction”, which is made of fresh plant materials that are rapidly decomposed and turn over within a few years. The “heavily occluded” fraction is composed of carbohydrates and humic materials that can remain indefinitely, pending lack of soil disturbance. The light fraction seems to be what changes spatiotemporally, and will change the most readily in response to management changes (Fynn et al., 2010).

      In the period of years to decades, land managers are concerned with the rate of which soil carbon is accumulated or released to the atmosphere. Modeling suggests that soil organic carbon accumulates over time in a non-linear manner. Lal proposes it follows a sigmoid curve, reaches the maximum sequestration rate 5-20 years after management changes and then settles into an equilibrium rate (Lal 2004). Climate has a large effect on the rate of sequestration- dry and warm regions have slower rates, upwards of 150 kG/ha/yr, while humid and cool climates could have rates up to 1000 kg/C/ha/yr (Lal 2004). One study estimates the time to reach equilibrium at up to 50 years after each disturbance (Batjes 1998). Simply put: after a change in management or some other disturbance alters the soil organic carbon pool, a new rate of sequestration (or emission) is set in motion and continues at this newly established rate until an equilibrium is reached, at which time the rate of sequestration/emission levels off and remains constant until the soil organic carbon pool “capacity” is reached. The rate is changed each time a new disturbance takes place, which is why it is crucial to keep management practices constant. Since our study takes place in a semi-arid Mediterranean climate, we hypothesize the rate of soil carbon pool accumulation will follow a slower curve than a tropical environment under the same management.

    • #Introduction

      Indirect measurements

      Modeling is generally incredibly useful to scale management changes and predict changes on a whole-systems scale. A 2004 French study utilized several modeling systems to demonstrate variabilities in soil carbon from a large database collected in 2002. The 19,000 unpublished references and 1000 literature references examined data taken from the upper 30 cm of soil and attempted to quantify fluxes in SOC stock and GHG changes to generalize conclusions regarding the kinetics of SOC accumulation (Soussana et al., 2004). However, quantifying the relationships between SOC pools and the related variables is challenging and convoluted. Storage of SOC is conventionally determined by the amount of net primary production that is allocated to belowground plant roots, while factoring in the effects of climate, biota, time, topography, and parent materials (Pineiro et al., 2010). The conceptual models estimate that changes in SOC stocks are determined by the balance between C and N inputs and outputs, respiration, and plant production, calculated as carbon outputs (Pineiro et al., 2010).
      Conventional models assume that the only carbon input in soils comes from biomass inputs from decomposition of surface litter and belowground roots (Jones, 2008). In other words, the models only consider the light fraction of carbon made of decomposing plant materials (Fynn et al., 2010), which is why most experimental models conclude high spatiotemporal variability and low rates of carbon sequestration that is easily released back into the atmosphere. Direct measurements are needed to better understand the dynamic and complex relationships between the components that determine soil carbon sequestration.

      The use of modeling to determine SOC sequestration capacity is in part limited by the inherent spatial variability in soils that limits the precision of measurements (Conant et al., 2002). Spatial variation is compounded by soil variation, microclimate, fire history, topography, and plant communities (Pringle et al., 2011). Soil carbon stocks in grasslands have higher spatial variability than crop land (Soussana et al., 2004), and forested areas have greater spatial variability than cultivated sites (Conant et al., 2002). It is difficult to distinguish between natural fluxes in carbon stocks due to the factors described above, and changes that are driven by land management. However, several statistical analyses have found that small changes in SOC are detectable with the proper controlled measurement (Conant et al., 2002). Donovan recommends waiting longer between samplings, at least a few years, to maximize the chance of detecting actual change, and distinguish between year-to-year variability (Donovan, 2013).

    • #Introduction

      The role of mycorrhizal fungi

      The missing link in carbon sequestration research may be the role of mycorrhizal fungi and humification in storing organic carbon. Mycorrhizal fungi is still relatively poorly understood, as they are exceedingly fragile, can take several years to establish, and are destroyed in seconds following herbicide application and physical disturbance like tilling (Allen, 2006). In addition, although the fungi networks can constitute 20-30% of the total soil microbial biomass, they are not detected by standard biomass sampling techniques and have remained fully undiscovered (Leake eta l., 2004). However, there can be several kilometers of hyphae present in a single gram of soil (Allen, 2006) and the structural complexity of mycelial networks is only recently discovered (Leake et al., 2004).
      Considered by some to be the most dynamic and diverse component of symbiosis (Leake et al., 2004), the simple role of myocorrhizal fungi is to transport nutrients to the plant in exchange for carbon in the form of sugars (Jones, 2008). The hyphae carry carbohydrates from plants into soil regions far deeper than the conventional root zone, and release exudates and other compounds to interact with deep soil microbiota (Leake et al., 2004).
      There is a crucial relationship between mycorrhizal hyphae exudates and carbon sequestration that has been largely overlooked by conventional modeling. Jones uses the term “liquid carbon pathway” to describe mycorrhizal hyphae’s ability to carry carbon deep into the soil, where it is humified into stable form that can remain there for hundreds of years (Jones, 2008). Arbuscular mycorrhizal fungi, conventionally considered as agriculturally important to soil fertility (Jones, 2008), secretes glomalin that accumulates in soil and contributes to a substantial proportion of stable SOC (Leake et al., 2004). Humic substances were once thought to be huge polymers, but now are suggested as being associations of small molecules held by weak forces that interact with organic compounds in soils (Spaccini et al., 2002). Carbon that is sequestered into the humic pool is protected from microbial degradation by the biochemical means described earlier, and may remain in the soil for hundreds of years (Spaccini et al., 2002).
      Conventional models of soil organic carbon sequestration assume that the only carbon inputs to soil are root decomposition, sloughed cells, (Leake et al., 2004) and surface decomposition. However, up to 15% of the soil organic carbon pool can be contributed by mycorrhizal fungi (Leake et al., 2004)- and that’s only based on the recent discoveries of hyphae networks whose relationships are not yet fully understood. The humified carbon that can form deep in the soil profile may prove the unseen contributor of carbon sequestration as a valid climate change mitigation strategy (Jones, 2008).

    • #Materials&Methods

      Measurements and sample sizing

      SOC sequestration can be estimated by directly measuring changes in carbon pools or indirectly by measuring carbon fluxes (Soussana et al., 2010). Five common laboratory techniques to measure soil carbon from a soil sample include elemental analysis by dry combustion, acid treatments, loss on ignition, carbon fractions, and soil respiration (Donovan, 2013). Of these, elemental analysis by dry combustion is considered the most accurate that is likely to detect change in the organic carbon fraction but measures total soil carbon (inorganic and organic) (Donovan, 2013). Since large quantities of carbon are already present in the soil, sensitive methods are needed to detect small changes (Ellert et al., 2002). Most SOC studies focus on the 0-30 cm soil strata (Soussana et al., 2010) because of the traditional thought that sequestration is brought about from decomposing surface litter and roots. For our study, we took measurements from three horizontal strata: 0-10 cm, 10-25 cm, and 25-40 cm.

      Cost and practicality are limiting factors when taking soil measurements, and for the purposes of this experiment we were limited to very few samples. However, Pringle et al found success with using 25 soil samples per unit to estimate baseline mean soil organic carbon to within 20% of the true mean to a depth of 30 cm (Pringle et al., 2011). A 2002 study found that six cores per microplot is adequate to represent a range of soil samples within more uniform sites (Conant et al., 2002). Sampling from different horizontal strata reduces variability since deeper layers have less spatiotemporal variation and can help to account for differences in soil types, vegetation cover, and management (Donovan, 2013). The power of testing microsites to make broad generalizations about an entire pasture is limited (Donovan, 2013), and taking samples from multiple microplots in the future will decrease variability (Conant et al., 2002).
      The purpose of our experiment was to establish a baseline SOC pool in two separate pastures to compare future carbon changes, if any. The same microplots will be samples in the future to enhance statistical power (Conant et al., 2002).

    • Our study

      We took soil samples from two pastures that represented the high and low quality spectrum of the ranch. Pasture 1 had been grazed periodically for several decades, had been irrigated since [ ] ?? and had limited traffic across of it. Pasture 2 had been eliminated from the grazing plan, but had been grazed periodically as needs changed. Pasture 2 was adjacent to the barn facility, and had an old silage cement bunker and a carport on it, so there has been considerably heavier vehicle traffic across the pasture.
      Biological monitoring
      The transects were chosen in a part of the pasture that seemed qualitatively representative of the entire pasture. Transect tape was laid down for 200m, and the center of the testing site was chosen at 50m. The transect was marked with physical guidelines (i.e. positions of utility poles, fence posts, and other physical characteristics that were not likely to change), compass bearing, and latitude/longitude bearings. The transect was divided into a 10m plot with sampling sites every 1 sq m.

      The purpose of our experiment is to establish a baseline amount of soil organic carbon in two pastures to compare future data. We chose two pastures that are close in physical proximity but differ in the grazing management applied to them. Our hypothesis is that the two pastures will contain different quantities of soil organic carbon in the 0-10 cm strata due to their different grazing management, but similar quantities in the 10-25 cm and 25-40 cm strata because of their proximity and similar soil types.

      The drylot pasture is located close to a riparian area and borders a barn which was a historic dairy. The pasture has a concrete silo for silage storage, and a large carport for storing tractors and machinery. Thus, the pasture has experienced more vehicle traffic than the irrigated pasture. The drylot pasture1 was largely left out of the planned grazing and used only when the sheep needed an overflow area for a day or two, so it has been grazed irregularly and overgrazed at times. It is not irrigated.
      The irrigated pasture is located on the opposite side of the barn from Pasture 1 and also borders a riparian area. It is irrigated regularly during dry summer months, and has been grazed by sheep using holistically planned short-duration, high-intensity rotational grazing. It is usually grazed with a stocking density of 60-90 ewes during the winter, or up to 100 lambs during the summer, and grazed for a period of 7-10 days before getting 45-50 days of rest.

      We collected soil samples in early December 2015 using a soil corer to take a 0-10 cm, 10-25 cm, and 25-40 cm sample from stratified simple random sites. See fig Donovan’s picture for placement of soil samples. The samples were oven-dried and ground with mortar and pestle to homogenize them, then poured through a 2mm sieve to remove rock and root debris. The samples were run through a CN element analyzer make and model.

    • #Discussion

      Grazing effects on soil carbon sequestration

      The impact that soil carbon sequestration might have on global soils is effectively useless if the rate of sequestration cannot be manipulated by human management. Luckily, the immense size of the global soil pool means that small changes in carbon pools can have drastic effects on the global climate system (Schlesinger, 1995). The substantial area of the globe utilized for grazing means that small changes in SOC can cause proportionately large changes in global carbon sequestration (Pringle et al., 2011). In California, grazing land makes up approximately half of land use (Silver et al., 2010). However, little is currently known about how cattle grazing affects SOC (Pringle et al., 2011).
      A 2010 global literature review found that SOC changed under contrasted grazing conditions across climactic gradients, and that the factors that control SOC in a grazed ecosystem are more complex than previously thought. General patterns that the study noted were that root contents were higher in grazer than ungrazed systems at the most arid and most tropical sites but were lower at temperate sites, and thought to increase soil carbon by increasing biomass decomposition (Pineiro et al., 2010). An analysis of 115 studies in pastures found that “light grazing” increased SOC more than exclosure and “heavy grazing” (Soussana et al., 2010). However, the article did not specify whether the heavily grazed pastures were on a continuous or rotational grazing system, or how the stocking density related to the carrying capacity of the specific pastures. Studies have found that SOC increases, decreases, or is relatively maintained in different grazing systems across climatic gradients, and the challenge is to understand the relationship between grazing management and soil carbon sequestration.
      Grazing is inherently difficult to describe in an experimental system because of the many different ways to graze pastures, the type of pasture that is being grazing, and abiotic climatic factors that affect the way grazing is conducted, as well as behavioral characteristics of grazing herbivore that affect aboveground and belowground communities. Jones states, “grazing animals, plants, soil biota and soils have co-evolved for over 20 million years, resulting in highly complex and sensitive inter-relationships” (Jones, 2006). There is no universal way to describe how grazing affects soil carbon sequestration, but the attempts are to broadly describe effects that should incentive producers to make changes that will enhance soil carbon sequestration rates.
      One very simple proposed method for how grazing soil carbon is how the plant readjusts for biomass loss after grazing. More carbon is contained in the roots than the leaves of the plant, and when the leaves are removed by grazing, and plant responds by readjusting its biomass balance. Some carbon is mobilized to the crown for production of new leaves, some is lost to the soil as root decomposition, and some is actively exuded into the rhizosphere. Thus, each grazing event becomes a “carbon injection” opportunity (Jones, 2008). However, much more research is indicated to examine different grazing management systems and their effects on soil microbial communities such as arbuscular mycorrhizal fungi. An efficient strategy to compile data is to educate and encourage producers to start their own carbon monitoring practices that can be compiled into open-source data networks, much like the Soil Carbon Coalition, a non-profit organization dedicated to sharing open-source data between producers (Donovan, 2015).
      We propose that in the ensuing five years, the amount of carbon contained in our pastures will change due to the grazing management applied to the pastures. The drylot pasture was incorporated into the grazing plan and will experience the same short-duration, high-intensity rotational grazing that the irrigated pasture is managed with, but with a smaller duration of time. We hypothesize that in five years, the carbon content of the drylot pasture will have increased in the 0-10 cm strata, and will likely increase in the 10-25 cm and 25-40 cm horizons due to more developed root systems whose relationship with mycorrhizal fungi channels carbon deeper into the soil profile. If grazing management, irrigation management, and soil disturbances are well managed, there should be an increase of carbon in the irrigated pasture as well. If management stays approximately the same, the carbon content in the irrigated pasture should reflect only natural fluxes.

    • #Discussion

      Best Management Practices

      Recent studies have suggested that making changes in land management can improve the rates of soil carbon sequestration. Soussana et al conducted a meta-analysis of 115 studies in pastures and grazing land and found that improved management increased SOC levels in 74% of the studies. Improved management practices included fertilization, grazing management, conversion from cultivation, and improved grass species (Soussana et al., 2010). However, little has been studied about the relationships between climate, stocking rates, grazing systems, and carbon dynamics (Fynn et al., 2010), and conventional grazing studies focus almost exclusively on continuous grazing systems. Some broadly drawn recommendations have been made, most originating from practices that have been solidly shown to improve factors that lead to improve soil carbon sequestration. In semi-arid grasslands, producers should reduce burning, control stocking rates, and improve nitrogen dynamics by avoiding excessive nitrogen inputs (Batjes 1998; Pineiro et al., 2010).
      Changing management practices to those that shift the soil biochemical environment to favor fungi can reduce the rates of SOC decomposition and enhance sequestration (Jones, 2008). Practices that show potential for accomplishing this include planting perennial species, reducing tillage, maintaining neutral soil pH, ensuring adequate drainage, and minimizing erosion (Jastrow et al., 2007).
      General grazing system management changes emerging in the realm of sustainability research show promise to improve soil carbon sequestration as well. These include adjustments in stocking rates, introduction of grasses on degraded lands, managing invasive species, reseeding grassland species, riparian zone restoration, and introduction of biochar to soils (Fynn et al., 2010). Our study will contribute longitudinal data on rotational grazing systems, which have not been studied in depth.
      An indirect method to improve soil carbon sequestration is to avoid the loss of soil organic carbon through soil disturbance. SOC loss is exaggerated in agricultural ecosystems with severe soil degradation (Lal, 2004) and especially exacerbated in dry and warm climates (Lal et al., 1995). Carbon loss from soils is emitted directly into the atmosphere and reduces soil quality and biomass productivity, and negatively impacts water quality (Lal, 2004).

    • #Conclusion

      Implications for carbon markets

      Carbon markets are an economically valid proposal to incentive the agricultural segment to reduce greenhouse gas emissions, soil carbon emissions, and to improve soil carbon sequestration on private and public land. The basic idea of a carbon market is to instill a financial incentive to producers to sequester soil organic carbon on their land. Increased soil carbon levels would be converted to verified emissions reductions to use within an offset market, cap and trade system, or other credit program (Fynn et al., 2010). Carbon markets have been in use since 2002, mostly in European Union countries (Lal, 2004). Quantifying “ecosystem services” is a complex and convoluted process, albeit necessary to quantify the value to human societies that natural capital resources bring (Lara et al., nd). It is important that to mention that the more we know about the relationships of carbon sequestration and grazing practices, the closer we move towards establishing carbon markets that provide incentive to producers to make changes that will simultaneously mitigate climate change.

      Conclusion

      The purpose of this study is to examine an economically viable, low-labor method to establish a baseline soil organic carbon pool while collecting baseline data for longitudinal analysis. We found that there were significant differences in SOC content between two pastures that are in close proximity but have been under differing grazing management, and that our small soil sample number of 32 total samples gives sufficient confidence to detect changes in the SOC pool, while sampling from different strata increases the chance of detecting change related to management changes. This is encouraging to land managers and producers who wish to establish their own carbon monitoring systems without the use of much funding or infrastructure in preparation for the establishment of a formal carbon market. More research is indicated to establish greater accuracy in a greater number of microsites, and increased core samples within microsites.
      There has been an explosive, global increase in focus on carbon sequestration. In December 2015, France unveiled its 4% Initiative, which is is a voluntary group of stakeholders committed to action plans that implement management practices to enhance the soil organic pool of France’s soils. The initiative’s plan of action included structuring for multipartner action programs to better manage for soil carbon, and funding for international research and scientific cooperation programs (Ministry of Agriculture, 2015). Generally, the recommended management practices to improve soil carbon are natural, cost-effective, and environmentally-friendly (Lal, 2004). While more governments and agricultural programs are becoming open to the idea of carbon sequestration as a viable way to restore degraded agricultural lands, more research is called for to better understand the relationships between agricultural systems and carbon dynamics. The scientific community needs to be open to new pathways of carbon flow, as we discover more about soil microbiota and their ecosystems (De Deyn et al., 2008). Producers should begin to implement their own carbon monitoring methods, both in preparation for impending carbon market systems and in tandem with soil improvement strategies. The research techniques delineated in Donovan’s “Measuring Soil Change” are low-cost strategies that producers can use with their own equipment and very little money to analyze soil carbon content with statistical validity (Donovan, 2013). Open-source data from individual producers could aid greatly in understanding the relationships between management changes and soil carbon pools, as there is a lack of published data from California in particular, namely in areas that are not in close proximity to agricultural research stations (Silver et al., 2010). There should be further research in establishing economically viable and statistically significant techniques to link land management to changes in soil carbon pools to better understand the effect of soil health on carbon sequestration, and carbon sequestration on soil health.

    {"cards":[{"_id":"668a6878c9dec51054000029","treeId":"641e9e3b83e7b085f200008f","seq":6824580,"position":0.5,"parentId":null,"content":"#Timeline Plan\n\n[ ] History of C seq\n[X] Donovan's work \n[ ] Most recent C seq \n[ ] Soil carbon coalition\n\n[ ] look up journals for formatting\n[ ] Put together Materials & Methods\n\n[X] Combine lit review and paper?\n[ ] Put together Results & Discussion\n[ ] Put together INtro\n[ ] Put together Conclusion\n[ ] Put together Abstract\n\n[ ] Format Minitab tables \n[ ] Soil Survey map with soil type, classification, management recommendation\n[ ] GIS map of sheep unit pastures? \n\n[ ] Format citations"},{"_id":"66be12eed93604202a00002a","treeId":"641e9e3b83e7b085f200008f","seq":6783928,"position":0.75,"parentId":null,"content":"##Introduction\n\n####Literature\n History of C Seq\n Different ways to model\n Impact of myc fungi\n Carbon Coalition & small-scale data\n####My research\n Sheep unit pastures\n Intensive rotational grazing\n"},{"_id":"670013b71b17cd5e39000051","treeId":"641e9e3b83e7b085f200008f","seq":6835680,"position":1,"parentId":"66be12eed93604202a00002a","content":"###Climate change\nBroad climate change statement\nWhat is carbon seqestration and how does it fit into the picture\nSpecifically: grasslands and carbon sequestration (statistics, etc.)\n"},{"_id":"687ac47d6f5e0eff7900009c","treeId":"641e9e3b83e7b085f200008f","seq":7452638,"position":0.5,"parentId":"670013b71b17cd5e39000051","content":"`##distinction between C seq and C pools... where to put?`\n\nThere is a semantic distinction between the terms \"carbon sequestration\" and \"soil carbon pool\". The soil organic pool is a measurement of carbon in a depth of soil at any given time, while sequestration refers to the act of pulling in carbon and storing it into the soils. Soil carbon pools can be thought of a single \"snapshot\" in a dynamic process of carbon sequestration."},{"_id":"670021d21b17cd5e39000057","treeId":"641e9e3b83e7b085f200008f","seq":6895238,"position":1,"parentId":"670013b71b17cd5e39000051","content":"###Climate Change- broad impact statement\nIn the next century, the world faces a 2 degrees C or greater air temperature increased if GHG are not curtailed (Waltman et al., 2010).\nFortunately, the agricultural sector has significant opportunities to mitigate GHG emissions, and currently one substantiated option is to increase carbon sequestration (Waltman et al., 2010).\n\nThe agriculture, forestry, and other land use sector contributes just under a quarter of anthropogenic GHG emissions, or 10-12Gt CO2 eq/year (Smith et al., 2014).\nThe agricultural sector is the largest contribute to global anthropogenic non-CO2 GHG at 56% in 2005- not including agricultural machinery use. Between 1990 and 2010, agricultural non-CO2 emissions grew by 0.9%/year (Smith et al,. 2014).\nEneteric fermentation and agricultural soils contribute to 70% of total agricultural emissions. Biomass burning accounts for 6-12%, and synethetic fertilization to 12% (Smith et al., 2014).\n\nThe International Panel on Climate Change predicts that the supply of primary energy will be dominated by fossil fuels until at least 2050 (IPCC, 2005).\n\nThe Lima-Paris Action Agenda, unveiled at the United Nation Climate Change Conference in November 2015, announced that the carbon farming movement is “moving forwards”. Targeting the Action Agenda’s goal of resilient societies with low carbon levels, it stated that a “growing” number of advocates say that “one of the best opportunities for drawing carbon back to Earth is for its land managers to sequester more carbon in the soil” (Bland, 2015)."},{"_id":"6838d2e12c07b5777d00008a","treeId":"641e9e3b83e7b085f200008f","seq":7395287,"position":2,"parentId":"670021d21b17cd5e39000057","content":"####Climate Change impact statement\n\nIn the next century, the world faces a 2 degree C or greater air temperature increase (Waltman et al., 2010). Climate change is an all-encompassing global `problem` that threatens food security, water availability, civil unrest, and more. The agricultural sector has significant opportunities to mitigate GHG emissions, and currently one substantiated option is to increase carbon sequestration (Waltman et al., 2010). \n\nThe International Panel on Climate Change predicts that the global energy supply will continue to be dominated by fossil fuels until at least 2050 (IPCC, 2005). That means that an alternative to mitigating GHG emissions must lie in another sector. Enteric fermentation and agricultural soils contribute to 76% of total agricultural emissions, while biomass burnings account for 6-12%, and synthetic fertilization for 12% (Smith et al., 2014). Carbon sequestration is hailed as the win-win situation for producers, land managers, environmentalists, and climate-change advocates. The Lima-Paris Action Agenda, unveiled at the United Nation Climate Change Conference in November 2015, called carbon sequestration \"one of the best opportunities for drawing carbon back to Earth\" (Bland, 2015). With the obvious necessity to make changes to the agricultural sector to avoid the catastrophic effects of climate change, it is pertinent to examine the effects of agricultural management practices on carbon sequestration. "},{"_id":"687a9e306f5e0eff7900009b","treeId":"641e9e3b83e7b085f200008f","seq":7439171,"position":1,"parentId":"6838d2e12c07b5777d00008a","content":"#Introduction\n\n**Introduction to carbon sequestration and grassland implications**\n\nIn the next century, the world faces a 2 degree C or greater air temperature increase (Waltman et al., 2010). Climate change threatens food security, water availability, civil unrest, and more (Lal, 2004). The agricultural sector has significant opportunities to mitigate greenhouse gas (GHG) emissions, and currently one substantiated option is to increase carbon sequestration (Waltman et al., 2010).\n\nThe International Panel on Climate Change predicts that the global energy supply will continue to be dominated by fossil fuels until at least 2050 (IPCC, 2005). An alternative to mitigating GHG emissions must be found by other means. Enteric fermentation and agricultural soils contribute to 76% of total agricultural emissions, while biomass burnings account for 6-12%, and synthetic fertilization for 12% (Smith et al., 2014). Carbon sequestration is regarded as a positive strategy for producers, land managers, environmentalists, and climate-change advocates. The Lima-Paris Action Agenda, unveiled at the United Nation Climate Change Conference in November 2015, called carbon sequestration “one of the best opportunities for drawing carbon back to Earth” (Bland, 2015). With the obvious necessity to make changes to the agricultural sector to avoid the catastrophic effects of climate change, it is pertinent to examine the effects of agricultural management practices on carbon sequestration.\n\nThe Department of Energy defines carbon sequestration as “the provision of long-term storage of carbon in the terrestrial biosphere, underground, or in the oceans so that the buildup of CO2 will reduce or slow.” (Lal, 2007). Simply put, it is the act of transferring atmospheric CO2 into pools elsewhere in the biosphere and storing it in a way that it is not immediately reemitted (Lal, 2004). Carbon sequestration can also refer to the act of increasing the SOC pool through changing land management practices (Lal, 2004). Sequestration can be natural or anthropogenic-driven. Anthropogenic sequestration methods include geological storage, ocean storage, and industrial fixation of CO2 in inorganic carbonates (IPCC, 2005). Natural sequestration is limited to soils and trees (Lal et al., 2007). Carbon sequestration was originally pulled into the climate change spotlight in the 1970s, when a study proposed that planting trees could offset carbon emissions (Ellert et al., 2002). Since then, we have discovered that the soil biome has unprecedented potential to capture carbon. Soil has tremendous ability to pull in carbon from the atmosphere and store it in soil as humified organic carbon (Jones, 2008).\n\nSoil carbon storage is a key component of the global carbon cycle (De Deyn et al., 2008). It is critical that we can quantify the ability of management changes to manipulate the carbon cycle to pull more carbon into the soil than is taken out of it. The estimated range of carbon sequestration that could potentially offset fossil fuel emissions varies widely in scientific literature, and seems largely dependent on what modeling technology is used. On the upper end, Lal estimates that with proper management changes, 0.4-1.2 Gt C/yr, or 5-15% of global fossil fuel emissions, can be sequestered (Lal, 2004). Each ton of stored carbon in soils removes 3.67 tons of CO2 from the atmosphere (Fynn et al., 2010).\nThe global soil organic carbon pool is 3.3 times the size of the atmospheric carbon pool, and 4.5 times the size of the biotic pool (Lal, 2004). Most global soils contain anywhere from 50-150 tons per hectare of carbon in the upper 100 cm (Lal, 2004). The potential for carbon sequestration, while finite, seems to be astonishingly large. Agricultural soils have lost an estimated 50 Gt of carbon (Soussana et al., 2010), largely through practices that erode or degrade soils. Modeling technology can help a great deal with predicting how global soils can change, but smaller, direct-measurement studies are needed to firmly establish trends in SOC pools.\n\nIn this study, we compared two pastures on a sheep grazing ranch at California Polytechnic State University San Luis Obispo. The pastures are characteristic of California's annual grasslands. Grasslands cover a quarter of the earth’s surface and contribute to the livelihoods of 800 million people (Soussana et al., 2010). They might well be the biome that is the most intimately associated with human life and productivity. Livestock uses 3.4 billion hectares of grazing land, and a quarter of global crop land is dedicated to growing livestock feed (Soussana et al., 2010). Grazed grasslands are generally under human management, which gives a the land owner or manager the unique ability to manipulate a variety of traits on their land that could potentially affect carbon sequestration. Grazing lands contain 10-30% of the world’s soil organic carbon (Whalen et al., 2003) and are a major focus of carbon sequestration research because they are typically rich in soil organic carbon. Grassland soils have soil characteristics that promote aggregate formation that microorganisms form into micro-aggregates, the form in which soil organic carbon stabilizes the longest (Soussana et al., 2010). Soil organic matter, a major determinant of the dark-colored soils and mollisols associated with grasslands, also determines soil fertility, water retention, and soil structure (Pineiro et al., 2010).\nThe soil organic carbon sequestration potential for cropland and grazing land in the United States is estimated to be 180 Mt SOC/yr (Lal et al., 2007). A small change in soil organic carbon could have a large impact on overall emission reduction, due to the large surface area represented by rangelands (Fynn et al., 2010). There is a large potential for research to quantify management practices that can improve soil carbon sequestration on grasslands, and the variable that we are manipulating is low-input grazing management. We hypothesize that by manipulating the stocking density, intensity and duration of grazing, irrigation management, and soil disturbances, we will see an increase in soil carbon pools in five years.\n\n"},{"_id":"687add1b6f5e0eff7900009d","treeId":"641e9e3b83e7b085f200008f","seq":7452615,"position":1.5,"parentId":"6838d2e12c07b5777d00008a","content":"#Introduction\n\n**Carbon sequestration biomechanics**\n\nTypically, soil organic carbon is measured in the top soil and in organic form. While carbon can be sequestered as secondary carbonates, the rate is low (Lal, 2004). Most accumulation happens in 0-30 cm soil depth, although slow accumulation and rapid loss can occur from deeper horizons (Soussana et al., 2010). Carbon is usually not measured in vegetation, because net primary productivity is either transferred to animals via grazing, taken from the land as crops, or returned to the soil as litter.\nThere are 3 forms of carbon in soil. The largest fraction is organic soil carbon, which is derived from living tissue. It is critical in the formation of soil aggregates but is typically the least stable form of carbon. Charcoal is derived from living tissue as well, so is considered organic and is also more resistant to decomposition. Inorganic soil carbon is the most stable form because it is protected from decomposition but typically changes at a slower rate (Donovan, 2013).\n\nOrganic carbon can remain in soils for hundreds of years if left undisturbed, and carbon dating placed substantial amounts of soil organic carbon in deeper layers of soil several millenia ago (Soussana et al., 2010). However, soil organic carbon that is not stabilized in soil is quickly emitted back into the atmosphere through microbial respiration and decomposition. The two fundamental ways that SOC is stabilized in soil, that we have so far discovered, it through biochemical and physical protection. Biochemical alteration is the process of transforming SOC to chemical forms that are resistant to decomposition (Jastrow et al., 2007). Positively charged SOC molecules are chemically bonded to negatively charged iron and clay anions (Fynn et al., 2010). Physical protection is the process by which biochemical “glues” like glomalin hold soil aggregates together (Fynn et al., 2010). In order words, SOC is occluded within aggregates, sequestered deep within tiny pores inaccessible to microbial decomposers (Jastrow et al., 2007). \n\nIf soil organic carbon is not protected, it is easily lost back into the atmosphere (Sousanna et al., 2010). Disturbances are a major source of carbon loss, and thus soil organic carbon pools deeper in the soil are farther from the microbial ecosystems that decompose surface organic matter (Soussana et al., 2010) which contributes to its low rates of flux over time.\n\nDifferent research suggests different mean residence times for soil organic carbon, and the type of carbon that is studied must be examined for accurate comparison. Fynn et al suggests that there are two types of carbon accumulated, each with different mean residence times. He terms the “light fraction”, which is made of fresh plant materials that are rapidly decomposed and turn over within a few years. The “heavily occluded” fraction is composed of carbohydrates and humic materials that can remain indefinitely, pending lack of soil disturbance. The light fraction seems to be what changes spatiotemporally, and will change the most readily in response to management changes (Fynn et al., 2010). \n\nIn the period of years to decades, land managers are concerned with the rate of which soil carbon is accumulated or released to the atmosphere. Modeling suggests that soil organic carbon accumulates over time in a non-linear manner. Lal proposes it follows a sigmoid curve, reaches the maximum sequestration rate 5-20 years after management changes and then settles into an equilibrium rate (Lal 2004). Climate has a large effect on the rate of sequestration- dry and warm regions have slower rates, upwards of 150 kG/ha/yr, while humid and cool climates could have rates up to 1000 kg/C/ha/yr (Lal 2004). One study estimates the time to reach equilibrium at up to 50 years after each disturbance (Batjes 1998). Simply put: after a change in management or some other disturbance alters the soil organic carbon pool, a new rate of sequestration (or emission) is set in motion and continues at this newly established rate until an equilibrium is reached, at which time the rate of sequestration/emission levels off and remains constant until the soil organic carbon pool “capacity” is reached. The rate is changed each time a new disturbance takes place, which is why it is crucial to keep management practices constant. Since our study takes place in a semi-arid Mediterranean climate, we hypothesize the rate of soil carbon pool accumulation will follow a slower curve than a tropical environment under the same management. "},{"_id":"689ab552b9b112e2fe00008c","treeId":"641e9e3b83e7b085f200008f","seq":7452632,"position":1.75,"parentId":"6838d2e12c07b5777d00008a","content":"#Introduction\n\n**Indirect measurements**\n\nModeling is generally incredibly useful to scale management changes and predict changes on a whole-systems scale. A 2004 French study utilized several modeling systems to demonstrate variabilities in soil carbon from a large database collected in 2002. The 19,000 unpublished references and 1000 literature references examined data taken from the upper 30 cm of soil and attempted to quantify fluxes in SOC stock and GHG changes to generalize conclusions regarding the kinetics of SOC accumulation (Soussana et al., 2004). However, quantifying the relationships between SOC pools and the related variables is challenging and convoluted. Storage of SOC is conventionally determined by the amount of net primary production that is allocated to belowground plant roots, while factoring in the effects of climate, biota, time, topography, and parent materials (Pineiro et al., 2010). The conceptual models estimate that changes in SOC stocks are determined by the balance between C and N inputs and outputs, respiration, and plant production, calculated as carbon outputs (Pineiro et al., 2010). \nConventional models assume that the only carbon input in soils comes from biomass inputs from decomposition of surface litter and belowground roots (Jones, 2008). In other words, the models only consider the light fraction of carbon made of decomposing plant materials (Fynn et al., 2010), which is why most experimental models conclude high spatiotemporal variability and low rates of carbon sequestration that is easily released back into the atmosphere. Direct measurements are needed to better understand the dynamic and complex relationships between the components that determine soil carbon sequestration.\n\nThe use of modeling to determine SOC sequestration capacity is in part limited by the inherent spatial variability in soils that limits the precision of measurements (Conant et al., 2002). Spatial variation is compounded by soil variation, microclimate, fire history, topography, and plant communities (Pringle et al., 2011). Soil carbon stocks in grasslands have higher spatial variability than crop land (Soussana et al., 2004), and forested areas have greater spatial variability than cultivated sites (Conant et al., 2002). It is difficult to distinguish between natural fluxes in carbon stocks due to the factors described above, and changes that are driven by land management. However, several statistical analyses have found that small changes in SOC are detectable with the proper controlled measurement (Conant et al., 2002). Donovan recommends waiting longer between samplings, at least a few years, to maximize the chance of detecting actual change, and distinguish between year-to-year variability (Donovan, 2013). "},{"_id":"689ac0bab9b112e2fe00008d","treeId":"641e9e3b83e7b085f200008f","seq":7452676,"position":1.875,"parentId":"6838d2e12c07b5777d00008a","content":"#Introduction\n\n**The role of mycorrhizal fungi**\n\nThe missing link in carbon sequestration research may be the role of mycorrhizal fungi and humification in storing organic carbon. Mycorrhizal fungi is still relatively poorly understood, as they are exceedingly fragile, can take several years to establish, and are destroyed in seconds following herbicide application and physical disturbance like tilling (Allen, 2006). In addition, although the fungi networks can constitute 20-30% of the total soil microbial biomass, they are not detected by standard biomass sampling techniques and have remained fully undiscovered (Leake eta l., 2004). However, there can be several kilometers of hyphae present in a single gram of soil (Allen, 2006) and the structural complexity of mycelial networks is only recently discovered (Leake et al., 2004).\nConsidered by some to be the most dynamic and diverse component of symbiosis (Leake et al., 2004), the simple role of myocorrhizal fungi is to transport nutrients to the plant in exchange for carbon in the form of sugars (Jones, 2008). The hyphae carry carbohydrates from plants into soil regions far deeper than the conventional root zone, and release exudates and other compounds to interact with deep soil microbiota (Leake et al., 2004).\nThere is a crucial relationship between mycorrhizal hyphae exudates and carbon sequestration that has been largely overlooked by conventional modeling. Jones uses the term “liquid carbon pathway” to describe mycorrhizal hyphae's ability to carry carbon deep into the soil, where it is humified into stable form that can remain there for hundreds of years (Jones, 2008). Arbuscular mycorrhizal fungi, conventionally considered as agriculturally important to soil fertility (Jones, 2008), secretes glomalin that accumulates in soil and contributes to a substantial proportion of stable SOC (Leake et al., 2004). Humic substances were once thought to be huge polymers, but now are suggested as being associations of small molecules held by weak forces that interact with organic compounds in soils (Spaccini et al., 2002). Carbon that is sequestered into the humic pool is protected from microbial degradation by the biochemical means described earlier, and may remain in the soil for hundreds of years (Spaccini et al., 2002). \nConventional models of soil organic carbon sequestration assume that the only carbon inputs to soil are root decomposition, sloughed cells, (Leake et al., 2004) and surface decomposition. However, up to 15% of the soil organic carbon pool can be contributed by mycorrhizal fungi (Leake et al., 2004)- and that’s only based on the recent discoveries of hyphae networks whose relationships are not yet fully understood. The humified carbon that can form deep in the soil profile may prove the unseen contributor of carbon sequestration as a valid climate change mitigation strategy (Jones, 2008)."},{"_id":"66f398986c36c33b0800004b","treeId":"641e9e3b83e7b085f200008f","seq":7395281,"position":1.75,"parentId":"670013b71b17cd5e39000051","content":"#Smith et al., 2014\n\nThe agriculture, forestry, and other land use sector contributes just under a quarter of anthropogenic GHG emissions, or 10-12Gt CO2 eq/year (Smith et al., 2014). \n\nThe agricultural sector is the largest contribute to global anthropogenic non-CO2 GHG at 56% in 2005- not including agricultural machinery use. Between 1990 and 2010, agricultural non-CO2 emissions grew by 0.9%/year (Smith et al,. 2014).\n\nEneteric fermentation and agricultural soils contribute to 70% of total agricultural emissions. Biomass burning accounts for 6-12%, and synethetic fertilization to 12% (Smith et al., 2014).\n\n"},{"_id":"670033ae1b17cd5e39000059","treeId":"641e9e3b83e7b085f200008f","seq":7113419,"position":2,"parentId":"670013b71b17cd5e39000051","content":"###Definition of carbon sequestration\n\nAgricultural soils have lost an estimated 50 Gt of carbon (Soussana et al., 2010).\n\nThe range at which C seq can offset fossil fuel emissions varies from studies depending on which modeling aspects they are focusing in on, but Dr. Rattan Lal puts the number at 0.4-1.2 Gt of carbon per year, or 5-15% of global fossil-fuel emissions (Lal, 2004). \n\n2500 Gt of carbon are contained in our world's soil organic carbon pool, of which 1550 Gt is organic and 950 Gt is inorganic. In comparison, it is 3.3 times atmospheric carbon levels and 4.5 times the size of the biotic pool (Lal, 2004). \n\nMost global soils range from 50-150 tons per hectare of carbon in the 100 cm depth (Lal, 2004).\n\nThe definition of C sequestration is the act of transferring atmospheric CO2 into long-lived pools and storing it securely in such a way that it’s not immediately reemitted (Lal, 2004). Carbon sequestration can also refer to the act of increasing the SOC pool through management practices (Lal, 2004).\n\n\n\nCarbon sequestration is a bridge between 3 global issues: climate change, desertification, and biodiversity (Lal, 2004). Regardless of the climate change debate, it is a crucial issue that could increase productivity and water quality and restore degraded ecosystems (Lal, 2004).\n\nAgriculturally developing nations, especially those in tropical climates where dynamic soil processes exacerbate rates of SOC accumulation or loss, have the greatest need for change. Currently, the C sink capacity is high, but the rate of C seq is low and complicated by limited infrastructure and resource-poor agricultural systems (Lal, 2004).\n\nGenerally, soil C seq by adapting recommended management practices is a natural, cost-effective, and environmentally-friendly process (Lal, 2004).\n\nIn essence, C seq is act of storing atmospheric carbon in the soil as humified organic carbon (Jones, 2008). \n\nOne of the first mentions of carbon sequestration were a 1977 study that proposed C emissions could be offset by planting massive quantities of trees (Ellert et al., 2002).\n\nSoil carbon storage is a key component of the global carbon cycle (De Deyn et al., 2008).\n\n\n###Definition carbon seq continued\n\n\nIt is thought that the maximum sequestration potential of soils is determined by intrinsic abiotic soil factors like topography, mineralogy, and texture, and that biota-driven factors are a minor factor in soil carbon dynamics (De Deyn et al., 2008).\n\n“Soil carbon measurement is as much a social issue, involving beliefs and attitudes, as it is a technical one” (Donovan, 2013)\nThe global issue of carbon has many contexts and perceptions, as well as different uses to people and producers (Donovan, 2013). This complicates the seemingly simple idea of measuring soil carbon change.\n“Carbon is life and food, and moves from atmosphere to plants and soils and back in a grand cycle that is sometimes called the circle of life” (Donovan, 2013).\n\nEneteric fermentation and agricultural soils contribute to 70% of total agricultural emissions. Biomass burning accounts for 6-12%, and synethetic fertilization to 12% (Smith et al., 2014).\n\nThe definition of carbon sequestration, according to the Department of Energy, is “the provision of long-term storage of carbon in the terrestrial biosphere, underground, or the oceans so that the build-up of CO2 will reduce or slow”. Sequestration is either natural or anthropogenic-driven. Natural sequestration is limited to terrestrial sequestration in soil and trees, while anthropogenic-driven geologic sequestration include such man-made technologies as injection of liquified CO2 into rock formations, old oil wells, etc. (Lal et al., 2007).\nSoil quality is defined as the combination of characteristics that enable soils to perform a wide range of functions (Lal et al., 2007).\nManagement choices affect the amount of soil organic matter, soil structure, soil depth, and water and nutrient-holding capacity (Lal et al., 2007).\n\nThe definition of C sequestration is the act of transferring atmospheric CO2 into long-lived pools and storing it securely in such a way that it’s not immediately reemitted (Lal, 2004). Carbon sequestration can also refer to the act of increasing the SOC pool through management practices (Lal, 2004).\n\nUS grazing lands could potentially sequester up to 198 million t CO2 /yr from atmosphere for 30 years (Fynn et al., 2010).\n\nEach ton of C stored in soils removes 3.67 t of CO2 from the atmosphere (Fynn et al., 2010)."},{"_id":"674b944e8529b4b146000077","treeId":"641e9e3b83e7b085f200008f","seq":7113284,"position":0.5,"parentId":"670033ae1b17cd5e39000059","content":"\n####Definition\n\nThe Department of Energy defines carbon sequestration as \"the provision of long-term storage of carbon in the terrestrial biosphere, underground, or in the oceans so that the buildup of CO2 will reduce or slow.\" (Lal, 2007). Simply put, it is the act of transferring atmospheric CO2 into pools elsewhere in the biosphere and storing it in a way that it is not immediately reemitted (Lal, 2004). \"Carbon sequestration\" can also refer to the act of increasing the SOC pool through changing land management practices (Lal, 2004). In terms of soil, sequestration refers to the abilities of soil to store atmospheric carbon in the soil as humified organic carbon (Jones, 2008).\n\nSequestration can be natural or anthropogenic-driven. Anthropogenic sequestration methods include geological storage, ocean storage, and industrial fixation of CO2 in inorganic carbonates (IPCC, 2005). Natural sequestration is limited to soils and trees (Lal et al., 2007). "},{"_id":"674b6ecf8529b4b146000076","treeId":"641e9e3b83e7b085f200008f","seq":7112380,"position":1,"parentId":"670033ae1b17cd5e39000059","content":"####History\n\nCarbon sequestration was first brought into the climate change spotlight in the 1970s, when a study proposed that planting trees could offset carbon emissions (Ellert et al., 2002). Since then, the idea of carbon sequestration has been evolved and refined to management-driven predictions of how manipulating the soil organic carbon pools can change CO2 levels in the atmosphere. \n\n"},{"_id":"674b955d8529b4b146000078","treeId":"641e9e3b83e7b085f200008f","seq":7113422,"position":1.5,"parentId":"670033ae1b17cd5e39000059","content":"####Implications\n\nSoil carbon storage is a key component of the global carbon cycle (De Deyn et al., 2008). By manipulating the carbon cycle to draw more carbon into the soil than is taken out of it, more and more research is showing abilities of management practices to mitigate climate change. Carbon sequestration is becoming a global issue with many contexts and uses throughout industries (Donovan, 2013). \n\nThe estimated range of carbon sequestration that could potentially offset fossil fuel emissions varies widely in scientific literature, and seems largely dependent on what modeling technology is used. Dr. Rattan Lal estimates that with proper management changes, 0.4-1.2 Gt C/yr, or 5-15% of global fossil fuel emissions, can be sequestered (Lal, 2004). Each ton of stored carbon in soils removes 3.67 tons of CO2 from the atmosphere (Fynn et al., 2010).\n\nThe global soil organic carbon pool is 3.3 times the size of the atmospheric carbon pool, and 4.5 times the size of the biotic pool (Lal, 2004). Most global soils contain anywhere from 50-150 tons per hectare of carbon in the upper 100 cm (Lal, 2004). The potential for carbon sequestration, while finite, seems to be astonishingly large for the amount of controversy surrounding it. Agricultural soils have lost an estimated 50 Gt of carbon (Soussana et al., 2010), largely through practices that erode or degrade soils. Modeling technology can help a great deal with predicting how global soils will change, but smaller, direct-measurement studies are needed to firmly establish trends in SOC pools.\n\n "},{"_id":"6700545e1b17cd5e3900005b","treeId":"641e9e3b83e7b085f200008f","seq":6835944,"position":4,"parentId":"670013b71b17cd5e39000051","content":"###Grasslands and carbon sequestration\n\nAnnual net ecosystem production of grasslands can be 1-6tC/ha/yr and is typically limited by water and/or nutrients (Soussana et al., 2004).\n\nGrasslands cover a quarter of the earth’s land surface (Soussana et al., 2010).\nRangelands are found on every continent and contribute to livelihoods of 800 million people. Livestock uses 3.4 billion hectares of grazing land, in addition to feed produced on a quarter of the world’s crop land (Soussana et al., 2010).\n\nAgricultural soils have lost an estimated 50 Gt of carbon (Soussana et al., 2010).\n\nGrassland soils are a major focus of carbon sequestration research, because they are typically rich in SOC. Grassland soils have active rhizodeposition and earthworm activity that promote aggregate formation that microbiota form into micro-aggregates, the form in which SOC stabilizes for extended periods (Soussana et al., 2010).\n\n“Grazing lands contain 10-30% of the world’s SOC and have potential to act as a significant sink of atmospheric CO2” (Whalen et al., 2003).\nThe Great Plains have lost 24-60% of their SOC pool from 100 years of cultivation, which breaks up soil aggregates and fragments organic matter, increasing the rate of decomposition and stimulating emission of CO2 from soils (Whalen et al., 2003).\nCrop systems have decreased C input since most above-ground biomass is removed and annual crops produce less root biomass than perennial plants (Whalen et al., 2003).\nConverting cropland to grasslands in semi-arid Great Plains don’t always work out as planned, although they can usually be restored by seeding non-native perennial grasses (Whalen et al., 2003). Understandably, total C, N, and microbial biomass are lower in recently established grasslands and can take over 50 years to approach native levels (Whalen et al., 2003).\n\n“Soil organic matter is the main reservoir of SOC and soil organic nitrogen in rangelands and determines soil fertility, water retention, and soil structure” (Pineiro et al., 2010)\nIn arid rangelands, SOC accumulation is limited by water availability and C uptake- also known as net primary productivity (Pineiro et al., 2010).\n\n“Rangelands trap and store carbon and thus reduce atmospheric greenhouse gases, store water, and filter impurities from water” (NRCS, 1996).\nAmerica’s rangelands deteriorated rapidly and significantly during the late 1800s (NRCS, 1996).\n\nPastures and rangelands cover 55% of United States’s total land surface, and represent the largest and most diverse resource in the world (Lal et al., 2007).\n\nThe SOC seq potential for US cropland and grazing land is 180Mt SOC/yr (Lal et al., 2007).\n\n13.6 million acres make up California annual grasslands, which subdivide into inland valley grassland, coastal prairie, and coast range grassland. The plant communities are now dominated by exotic annual grasses brought from Mediterranean regions by Spanish explorers (Fynn et al., 2010).\n\nThe term “rangelands” includes grasses, savannas, steppes, shrub lands, desert, and tundra (Fynn et al., 2010).\nA small change in SOC could have a large impact on overall GHG, since US rangelands represent such a large surface area (Fynn et al., 2010).\nUS grazing lands could potentially sequester up to 198 million t CO2 /yr from atmosphere for 30 years (Fynn et al., 2010).\nEach ton of C stored in soils removes 3.67 t of CO2 from the atmosphere (Fynn et al., 2010).\nSOC is 50% of soil organic matter (Fynn et al., 2010).\nManagement recommendations made by Flynn et al for increased carbon sequestration include adjustments in stocking rates, introduction of grasses on degraded lands, managing invasive species, reseeding grassland species, riparian zone restoration, and introduction of biochar to soils (Fynn et al., 2010).\n\n\n90% of carbon in rangeland systems is in the soil (Fynn et al., 2010).\n\nIn grasslands, three major greenhouse gases are exchanged at the atmosphere-biosphere level. Carbon dioxide is exchanged with soil and vegetation, nitrous oxide is released by soils, and methane is emitted with livestock and can be taken in by soils (Soussana et al., 2004)."},{"_id":"674ca3ff3b6c0dac06000078","treeId":"641e9e3b83e7b085f200008f","seq":7113423,"position":1,"parentId":"6700545e1b17cd5e3900005b","content":"####Why grasslands\n\nGrasslands cover a quarter of the earth's surface, are found on every continent, and contribute to the livelihoods of 800 million people (Soussana et al., 2010). They might well be the biome that is the most intimately associated with human life and productivity. Livestock uses 3.4 billion hectares of grazing land, and a quarter of global crop land is dedicated to growing livestock feed (Soussana et al., 2010). Grazed grasslands are generally under close human management, which gives a single producer the unique ability to manipulate a variety of traits on their land that could potentially affect carbon sequestration. Grazing lands contain 10-30% of the world's soil organic carbon (Whalen et al., 2003). \n\nGrasslands are a major focus of carbon sequestration research because they are typically rich in soil organic carbon. Grassland soils have soil characteristics that promote aggregate formation that microorganisms form into micro-aggregates, the form in which soil organic carbon stabilizes the longest (Soussana et al., 2010). Soil organic matter, a major determinant of the dark-colored soils and mollisols associated with grasslands, also determines soil fertility, water retention, and soil structure (Pineiro et al., 2010). \n\nThe soil organic carbon sequestration potential for cropland and grazing land in the United States is 180 Mt SOC/yr (Lal et al., 2007). A small change in soil organic carbon could have a large impact on overall emission reduction, due to the large surface area represented by rangelands (Fynn et al., 2010). "},{"_id":"674ca4aa3b6c0dac0600007a","treeId":"641e9e3b83e7b085f200008f","seq":7439044,"position":3,"parentId":"6700545e1b17cd5e3900005b","content":"####Our grassland\n\n"},{"_id":"670016161b17cd5e39000052","treeId":"641e9e3b83e7b085f200008f","seq":6835712,"position":2,"parentId":"66be12eed93604202a00002a","content":"####Biomechanics of carbon sequestration\n\nNatural vs anthropogenic\n3 ways of natural seq: litter decomposition, root decomposition, root exudates\nLongevity and protecting it from decomposition\n"},{"_id":"6700cc9c1b17cd5e3900005d","treeId":"641e9e3b83e7b085f200008f","seq":7113500,"position":2,"parentId":"670016161b17cd5e39000052","content":"###Biomechanics: 3 ways of natural sequestration\n\nWhile C can be sequestered as secondary carbonates, that rate is low and not the subject of focus as much as SOC is (Lal, 2004).\nWhile soil carbon sequestration may not be the end-all of climate change solutions, it shows potential to mitigate the effects of climate change until fossil fuel alternatives take effect (Lal, 2004).\n\nMany SOC studies focus on the 0-30cm soil strata, as most accumulation occurs in those layers, but lose can occur from deeper horizons (Soussana et al., 2010).\n\nSoil has 2.5 times more organic C than vegetation and twice the C than the atmostphere (Batjes 1998).\n\nThe topsoil organic matter is involved in nutrient cycling and atmospheric gas exchange (Batjes 1998).\n\nSoil organic matter characteristics are influenced by moisture status, soil temperature, oxygen supply (drainage), soil acidity, soil nutrient supply, clay content, and mineralogy (Batjes 1998).\n\nGeneral plant traits regulate SOC by altering carbon input through NPP and belowground carbon allocation (De Deyn et al., 2008).\n\nFast-growing plant species contribute carbon through root exudate to the soil, while slow-growing species contribute through input of low quality plant material. In biomes with a short growing season and low nutrient availability, SOC input is mainly derived from litter decomposition, but in productive biomes NPP is the main driver of carbon sequestration (De Deyn et al., 2008).\n\nThere are 3 forms of carbon in soil. The largest fraction is organic soil carbon, which is derived from living tissue. It is critical in the formation of soil aggregates but is typically the least stable form of carbon. Charcoal is derived from living tissue as well, so is considered organic and is also more resistant to decomposition. Inorganic soil carbon is the most stable form because it is protected from decomposition but typically changes at a slower rate (Donovan, 2013).\n\nIt is thought that the maximum sequestration potential of soils is determined by intrinsic abiotic soil factors like topography, mineralogy, and texture, and that biota-driven factors are a minor factor in soil carbon dynamics (De Deyn et al., 2008).\n\n"},{"_id":"674cbed63b6c0dac0600007b","treeId":"641e9e3b83e7b085f200008f","seq":7113507,"position":1,"parentId":"6700cc9c1b17cd5e3900005d","content":"####Forms of carbon in soil\n\nTypically, soil organic carbon is measured in the top soil and in organic form. While carbon can be sequestered as secondary carbonates, the rate is low (Lal, 2004). Most accumulation happens in the 0-30 cm soil strata, although slow accumulation and rapid loss can occur from deeper horizons (Soussana et al., 2010). Carbon is usually not measured in vegetation, because net primary productivity is either transferred to animals via grazing, taken from the land as crops, or returned to the soil as litter. \n\n\nThere are 3 forms of carbon in soil. The largest fraction is organic soil carbon, which is derived from living tissue. It is critical in the formation of soil aggregates but is typically the least stable form of carbon. Charcoal is derived from living tissue as well, so is considered organic and is also more resistant to decomposition. Inorganic soil carbon is the most stable form because it is protected from decomposition but typically changes at a slower rate (Donovan, 2013)."},{"_id":"6700ccfe1b17cd5e3900005e","treeId":"641e9e3b83e7b085f200008f","seq":7114000,"position":3,"parentId":"670016161b17cd5e39000052","content":"###Biomechanics: Longevity & protecting from decomposition\n\nSoil carbon stocks in grasslands have higher spatial variability than crop land (Soussana et al., 2004). Conversion of grassland to arable land can cause a 25-43% decline in SOC from 0-120 cm. However, converting cropland to grassland can reverse the decline and increase SOC by 0.5tC/ha/yr. Sousanna et al proposes that the rate of SOC growth in situation is slow and does not regain the level it held before the grassland was first plowed after 50 years.\n\nSOC accumulates over time in a non-linear fashion. Soussana et al estimates that converting cropland back to grassland for 20 years restores 18% of native C stocks in moist climates and 7% in temperate dry climates (Soussana et al., 2010).\n\nThe rate of turnover of organic matter can range from 15-40 years in the upper 10 cm and over 100 year for subsoil below 25 cm (Batjes 1998).\n\nIt can take from 10 to 50 years after each disturbance to resolve a new equilibrium of soil carbon (Batjes 1998). The equilibrium established after implementation of new land management can be lower or higher than the original amount.\n\nVariables controlling soil C seq, like climate change and rising atmospheric levels of CO2, are “highly interactive and complex” and, simply put, there are no easy answers (Batjes 1998).\n\nSOC can stay in soils for hundreds of years if left undisturbed (Soussana et al., 2010).\n\nNative prairie soil sites in the US Great Plains were subjected to 14C-dating that found mean residence time of SOC in soil increased but the concentration decreased with depth- however, “substantial amounts of SOC” were dated back several millenia (Soussana et al., 2010).\n\nSOC needs protection from microbial decomposition in order to stabilized long-term. SOC in deeper soils is distanced from the energy supply from decomposing surface organic matter. When tilling mixes soil layers and breaks up soil aggregates, it also accelerates SOC decomposition and prevents stable SOC sequestration (Soussana et al., 2010).\n\nThe rate of increasing SOC pools is nonlinear. Lal suggests it follows a sigmoid curve, hits the maximum rate 5-20 years after management changes and then continues until the SOC falls into equilibrium. Rates are inherently dependent on soil characteristics and climate as well as management. Dry and warm regions are subject to slower rates, upwards rates of 150 kG/ha/yr, while humid and cool climates could see C seq rates upward of 1000 kg/C/ha/year (Lal, 2004). These rates could potentially be sustained until the soil sink capacity is filled.\n\nBiochemical alteration is the process of transforming SOC to chemical forms that are more resistant to decomposition and are incorporated into soil solids (Jastrow et al., 2007).\n\nPhysicochemical protection is the ability of organomineral interactions to protect SOC from biochemical attack (decomposition) (Jastrow et al., 2007).\n\nThere are several ways to stabilize SOC to protect it from decomposition. These include occluding SOC within aggregates, depositing it in pores inaccessible to decomposers, and sorption ?? to mineral and organic soil surfaces (Jastrow et al., 2007).\n\nThere are 3 major ways to protect soil organic carbon from microbial decomposition. Chemical stabilization is the bonding of positively charged SOC molecules to negatively charged iron and clay anions. Physical protection is holding soil aggregates together with “glues” like glomalin, and biochemical recalcitrance is characteristics of carbon substrates that are consumed by microbes but remain un-decayed compounds (Fynn et al., 2010).\n\nTwo types of carbon in each accumulated pool have different mean residence times. The light fraction, made of fresh plant materials subject to rapid decomposition, turnover within a few years at most. Early changes in SOC from management changes occur in this fraction, which is also known for its high spatiotemporal variability. The heavily occluded fraction, composed of carbohydrates and humic materials stabilized in clay complexes, can remain in soil for hundreds to over a thousand years (Fynn et al., 2010).\nTypically, soils accumulated carbon during plant growth and lose carbon during dormancy (Fynn et al., 2010)."},{"_id":"674ccdca3b6c0dac0600007e","treeId":"641e9e3b83e7b085f200008f","seq":7395277,"position":0.5,"parentId":"6700ccfe1b17cd5e3900005e","content":"####Nonlinear acquisition of C\n\nModeling suggests that soil organic carbon accumulates over time in a non-linear manner. Lal proposes it follows a sigmoid curve, reaches the maximum sequestration rate 5-20 years after management changes and then falls into an equilibrium rate (Lal 2004). Climate has a large effect on the rate of sequestration- dry and warm regions have slower rates, upwards of 150 kG/ha/yr, while humid and cool climates could have rates up to 1000 kg/C/ha/yr (Lal 2004). One study estimates the time to reach equilibrium at up to 50 years after each disturbance (Batjes 1998). Simply put: after a change in management or some other disturbance alters soil organic carbon pool, a new rate of sequestration (or emission) is set in motion and continues at the new kinetic rate until an equilibrium is reached, at which time the rate of sequestration/emission levels off and remains constant until the soil organic carbon pool \"capacity\" is reached. The rate is changed each time a new disturbance takes place, which is why it is crucial to keep management practices `steady- new word` while the new rate is setting pace for sequestration.\n\n \n\n"},{"_id":"674ccb343b6c0dac0600007c","treeId":"641e9e3b83e7b085f200008f","seq":7395262,"position":1,"parentId":"6700ccfe1b17cd5e3900005e","content":"####Protecting from decomposition\n\nOrganic carbon can remain in soils for hundreds of years if left undisturbed, and carbon dating placed substantial amounts of soil organic carbon in deeper layers of soil several millenia ago (Soussana et al., 2010). However, soil organic carbon that is not stabilized in soil is quickly emitted back into the atmosphere through microbial respiration and decomposition. The two major ways that SOC is stabilized in soil, that we have so far discovered, it through biochemical and physical protection. Biochemical alteration is the process of transforming SOC to chemical forms that are resistant to decomposition (Jastrow et al., 2007). Positively charged SOC molecules are chemically bonded to negatively charged iron and clay anions (Fynn et al., 2010). Physical protection is the process by which biochemical \"glues\" like glomalin hold soil aggregates together (Fynn et al., 2010). In order words, SOC is occluded within aggregates, sequestered deep within tiny pores inaccessible to microbial decomposers (Jastrow et al., 2007). "},{"_id":"674ccb813b6c0dac0600007d","treeId":"641e9e3b83e7b085f200008f","seq":7395271,"position":2,"parentId":"6700ccfe1b17cd5e3900005e","content":"####How long C stays in soil\n\nSoil organic carbon can be easily lost back into the atmosphere if it is not properly protected from microbial decomposition (Soussana et al., 2010). SOC in deeper soils is farther from the major microbial communities and energy that decomposes surface organic matter (Soussana et al., 2010), which contributes to its relatively low rates of flux throughout time. \n\nDifferent research suggests different mean residence times for soil organic carbon, and the type of carbon that is studied must be examined for accurate comparison. Fynn et al suggests that there are two types of carbon accumulated, each with different mean residence times. He terms the \"light fraction\", which is made of fresh plant materials that are rapidly decomposed and turn over within a few years. The \"heavily occluded\" fraction is composed of carbohydrates and humic materials that can remain in soils for indefinite periods of time, pending that the soil remains undisturbed. The light fraction seems to be what changes spatiotemporally, and will change the most readily in response to management changes (Fynn et al., 2010). "},{"_id":"67001acb1b17cd5e39000053","treeId":"641e9e3b83e7b085f200008f","seq":6835682,"position":3,"parentId":"66be12eed93604202a00002a","content":"####Variability and controversy\n\nModels that are telling us to sequester very little\nSpatiotemporal variability in topsoil\n"},{"_id":"6700cda11b17cd5e3900005f","treeId":"641e9e3b83e7b085f200008f","seq":6895313,"position":1,"parentId":"67001acb1b17cd5e39000053","content":"###Variability: Models\n\nA 2004 French study utilized several modeling systems to demonstrate variabilities in a large database collected in 2002. The INRA ?? collected 19,000 unpublished references and 1000 literature references to pool data taken from the upper 30 cm of soil. The models attempted to quantify the fluxes in SOC stock and GHG changes, and generalized conclusions regarding the kinetics of SOC accumulation. The kinetics of SOC accumulation following changes in management practices appear to be non-linear and assymetric: the change is more rapid in the early years after changing land management, and accumulation is much slower than the previous release under the first management regime (Soussana et al., 2004).\n\n\nConceptual models estimate that changes in SOC stocks are determined by the balance between C and N inputs and outputs, more directly by NPP, respiration, and carbon outputs (plant production). Storage of SOC is determined by the proportion of NPP that is allocated to belowground organs. Climate, biota, time, topography, and parent materials are other factors that control SOC accumulation. Pineiro et al suggests that these contextual factors operate via cascade effects through shorter-term controls (Pineiro et al., 2010).\n\nMost conventional SOC models assume that the only C input in soils comes from biomass inputs from decomposition of surface litter and belowground roots. However, when carbon enters soil as plant material, it decomposes and is returned to the atmosphere as carbon dioxide (Jones, 2008).\n\nDirect methods of SOC measure directly from a soil sample, while indirect methods rely on modeling to predict the relationship between variable and carbon content (Fynn et al., 2010),\n\nThree uses of indirect measurement methods may assist in verifying direct measurement findings. They include the use of process-based or mechanistic models, remote sensing via satellite, and land use history and databases (Fynn et al., 2010)."},{"_id":"6838e72a2c07b5777d00008b","treeId":"641e9e3b83e7b085f200008f","seq":7395292,"position":1,"parentId":"6700cda11b17cd5e3900005f","content":"####Models & their Variabilities\n\nModels that attempt to predict the rates and amounts of carbon that agricultural land can sequester are incredibly useful, and simultaneously flawed beyond useful accuracy. A 2004 French study utilized several modeling systems to demonstrate variabilities in a large database collected in 2002. The 19,000 unpublished references and 1000 literature references examined data taken from the upper 30 cm of soil and attempted to quantify fluxes in SOC stock and GHG changes to generalize conclusions regarding the kinetics of SOC accumulation (Soussana et al., 2004). The great benefit of conceptual models is the ability to collect and analyze `huge` amounts of data at one time, which will prove to be an invaluable tool when producers are looking to make changes on large tracts of land. \n \nHowever, quantifying the relationships between SOC pools and the related variables is challenging and convoluted. Storage of SOC is typically determined by the amount of net primary production that is allocated to belowground plant roots, while factoring in the effects of climate, biota, time, topography, and parent materials (Pineiro et al., 2010). The conceptual models estimate that changes in SOC stocks are determined by the balance between C and N inputs and outputs, respiration, and plant production- seen as carbon outputs (Pineiro et al., 2010). The models assume that abiotic and management-driven factors operate via cascade effects through shorter-term controls (Pineiro et al., 2010). \n\nThese conventional models assume that the only carbon input in soils comes from biomass inputs from decomposition of surface litter and belowground roots (Jones, 2008). In other words, the models only consider the light fraction of carbon made of decomposing plant materials (Fynn et al., 2010), which is why most experimental models conclude high spatiotemporal variability and low rates of carbon sequestration that is easily released back into the atmosphere. \n\n"},{"_id":"66cb190c48d5a85245000041","treeId":"641e9e3b83e7b085f200008f","seq":7395288,"position":1.5,"parentId":"67001acb1b17cd5e39000053","content":"#Lara et al., nd\n\nQuantifying \"ecosystem services\" is a complex and convoluted process, albeit necessary to quantify the value to human societies that natural capital resources bring. Modern agriculture is a \"major driver of global environment change\" and there are numerous efforts to establish sophisticated economic models to predict global effects of carbon sequestration efforts. These include ARIES (artificial intelligence for ecosystem services) which takes open source data into account, InVEST (integrated valuation of ecosystem services and tradeoffs) which provides maps of monetary value among other outputs, and MAgPIE (Model of agricultural production and its impact on the environment) which shows potential output of carbon storage in soils and crop residue, etc (Lara et al, nd). These are just a few of numerous modeling systems that could be of future use towards establishing a global or domestic carbon market."},{"_id":"6700cde31b17cd5e39000060","treeId":"641e9e3b83e7b085f200008f","seq":6895268,"position":2,"parentId":"67001acb1b17cd5e39000053","content":"###Variability: Spatiotemporal\n\nSoil carbon stocks in grasslands have higher spatial variability than crop land (Soussana et al., 2004). Conversion of grassland to arable land can cause a 25-43% decline in SOC from 0-120 cm. However, converting cropland to grassland can reverse the decline and increase SOC by 0.5tC/ha/yr. Sousanna et al proposes that the rate of SOC growth in situation is slow and does not regain the level it held before the grassland was first plowed after 50 years.\n\n\nSpatial variation is further compounded by inherent soil variation, microclimate, fire history, tropography, and complex plant communities, which makes even the smallest scale of management tricky to sample precisely (Pringle et al., 2011).\n\nSoil carbon is tricky to detect and quantify, largely to due inherent spatial variability that limits precision the ability to detect change (Conant et al., 2002).\n\nConant et al compared samples from 4 sites of unique climatic and management combinations, and found that small changes in SOC are detectable, but only with careful and controlled measurement (Conant et al., 2002).\n\nThey found greater spatial variabilities in forested areas than cultivated sites (Conant et al., 2002).\n\nThe major sources of uncertainty in SOC sampling is sampling error and non-random selection of sampling sites (Donovan 2013).\n\nTo maximize the chance of detecting and measuring change, Donovan recommends waiting longer between samplings (Donovan, 2013). This would also aid to distinguish between year-to-year weather variability (Donovan, 2013)."},{"_id":"683900632c07b5777d00008c","treeId":"641e9e3b83e7b085f200008f","seq":7395300,"position":1,"parentId":"6700cde31b17cd5e39000060","content":"####Spatiotemporal variability\n\nThe use of modeling to determine SOC sequestration capacity is in part limited by the inherent spatial variability in soils that limits the precision of measurements (Conant et al., 2002). Spatial variation is compounded by soil variation, microclimate, fire history, topography, and plant communities (Pringle et al., 2011). Soil carbon stocks in grasslands have higher spatial variability than crop land (Soussana et al., 2004), and forested areas have greater spatial variability than cultivated sites (Conant et al., 2002). It is difficult to distinguish between natural fluxes in carbon stocks due to the factors described above, and changes that are driven by land management. However, several statistical analyses have found that small changes in SOC are detectable with the proper controlled measurement (Conant et al., 2002). Donovan recommends waiting longer between samplings, at least a few years, to maximize the chance of detecting actual change, and distinguish between year-to-year variability (Donovan, 2013). "},{"_id":"67001bf51b17cd5e39000054","treeId":"641e9e3b83e7b085f200008f","seq":6835685,"position":4,"parentId":"66be12eed93604202a00002a","content":"####The untold role of mycorrhizae\n\nChristine Jone's \"liquid carbon pathway\"\nWhat myc fungi does\nWhy we haven't put it in the equation\nWhy it means modeling might be wrong\nWhat's the only way to tell? More sampling on smaller scales"},{"_id":"6700ce391b17cd5e39000061","treeId":"641e9e3b83e7b085f200008f","seq":6895255,"position":1,"parentId":"67001bf51b17cd5e39000054","content":"###Mycorrhizal/Humification\n\nIn its most simple form, humification is joining simple carbon compounds together into more complex and stable molecules. It requires soil microbiota including mycorrhizal fungi, nitrogen fixing bacteria, and phosphorus solubilizing bacteria (Jones, 2008).\n\n\n\n“Soluble carbon” is the idea of simple sugars from the plant being channeled into soil aggregates via the hyphae of mycorrhizal fungi, and can be rapidly stabilized by humification (Johnes, 2008).\n\nMycorrhizal fungi is recognized in the agricultural world as decomposing fungi that obtains energy from decomposing organic matter and important for soil fertility and structure (Jones, 2008). Conventionally managed agricultural systems only see mycorrhizal fungi with small hyphal networks, because soil-disturbing acts like plowing and fungicide destroys the hyphae networks.\n\nMycorrhizal fungi transports nutrients, including P, K, and Zn, in exchange for carbon from their plant hosts. They connect individual plants below ground and can facilitate transfer of nutrients between species (Jones, 2008).\nHumification forms a stable and inseparable part of the soil matrix that can remain intact for hundreds of years (Jones, 2008).\n\nHumus differs from the labile pool of soil organic carbon that forms in the topsoil. Labile carbon is formed from biomass inputs, and humified carbon is secreted from exudation from plant roots to mycorrhizal fungi and microflora, and can form deep in the soil profile (Jones, 2008).\n\nConsidering the so-called “liquid carbon pathway”, C seq rates can range from 5-20 tCO2/ha/year (Jones, 2008).\n\nMycorrhizal fungi and nitrogen fixing bacteria are common plant symbionts that can increase plant productivity by attaining and transfering resources (De Deyn et al., 2008).\n\nMF enhances plant nutrient acquisition from soil, reduces soil C loss by immobilizing carbon in the myeclium, extending root lifespan, and importing C to soil aggregates, and are conveniently associated with most terrestrial plant species (De Deyn et al., 2008)."},{"_id":"6839106c2c07b5777d00008d","treeId":"641e9e3b83e7b085f200008f","seq":7395367,"position":1,"parentId":"6700ce391b17cd5e39000061","content":"####Mycorrhizae and humification\n\nA glaring error in early carbon sequestration research is the absence of the role of mycorrhizal fungi and humification in storing organic carbon. Mycorrhizal fungi is still relatively poorly understood, as they are exceedingly fragile, can take several years to establish, and are destroyed in seconds following herbicide application and physical disturbance like tilling (Allen, 2006). In addition, although the fungi networks can constitute 20-30% of the total soil microbial biomass, they are not detected by standard biomass sampling techniques and have remained fully undiscovered (Leake eta l., 2004). However, there can be several kilometers of hyphae present in a single gram of soil (Allen, 2006) and the structural complexity of mycelial networks is only recently discovered (Leake et al., 2004). \n\nConsidered by some to be the most dynamic and diverse component of symbiosis (Leake et al., 2004), the simple role of myocorrhizal fungi is to transport nutrients to the plant in exchange for carbon in the form of sugars (Jones, 2008). Generally stated, the hyphae carry carbohydrates from plants into soil regions far beyond the typical rhizosphere, and release exudates and other compounds to interact with deep soil microbiota (Leake et al., 2004). \n\nThere is a crucial link between mycorrhizal hyphae exudates and carbon sequestration that has been largely overlooked by conventional modeling. Christine Jones has coined the term, \"liquid carbon pathway\" to describe the abilities of mycorrhizal hyphae to carry carbon deep into the soil, where it is humified into stable form that can remain there for hundreds of years (Jones, 2008). Arbuscular mycorrhizal fungi, conventionally considered as agriculturally important to soil fertility (Jones, 2008), secretes glomalin that accumulates in soil and contributes to a substantial proportion of stable SOC (Leake et al., 2004). Humic substances were once thought to be huge polymers, but now are suggested as being associations of small molecules held by weak forces that interact with organic compounds in soils (Spaccini et al., 2002). Humification is a process that requires mycorrhizal fungi, nitrogen fixing bacteria, and phosphorus solubilizing bacteria (Jones, 2008). Carbon that is sequestered into the humic pool is protected from microbial degradation by the biochemical means described early in this article (Spaccini et al., 2002). The most impactful `part` of this relationship may be the proposal that humified soil organic carbon has an average residence time in soil of several hundreds of years (Spaccini et al., 2002). \n\nConventional models of soil organic carbon sequestration rest upon the assumption that the only carbon inputs to soil are root decomposition, sloughed cells, (Leake et al., 2004) and surface decomposition provide the only significant carbon inputs to soils. However, up to 15% of the SOC stock can be contributed by mycorrhizal fungi (Leake et al., 2004)- and that's only based on the recent discoveries of hyphae networks whose relationships are not yet fully understood. The humified carbon that can form deep in the soil profile may prove the unseen savior of carbon sequestration as a valid climate change mitigator (Jones, 2008). "},{"_id":"66c9a70948d5a8524500003a","treeId":"641e9e3b83e7b085f200008f","seq":7395302,"position":2,"parentId":"67001bf51b17cd5e39000054","content":"#Leake et al., 2004\n\nOne study refers to mycorrhizal fungi as the \"most dynamic and functionally diverse components of symbiosis\" (Leake et al., 2004). \n\nMycorrhizal fungi can constitute 20-30% of the total soil microbial biomass, but are not detected by standard measures of biomass (Leake et al., 2004). \n\nSome plants depend exclusively on MF for carbon (Leake et al., 2004).\n\nMF are highly sensitive to soil disturbance, and so the process to observe MF is difficult and complicated (Leake et al., 2004). \n\nMF gain direct access to plant-exudated sugars, giving it energy \"unparalleled\" amongst soil microbiota populations (Leake et al., 2004). \n\n\"most recent models of C fluxes between herbaceous plants and soil have been based upon the assumption that root exudation, sloughed cells and dead roots provide the only significant pathway for the supply of plant-fixed C to the free-living microbial populations in soils\" (Leake et al., 2004). \n\nOne estimate suggests that as much as 15% of SOC stock is contributed by arbuscular mycorrhizal fungi (Leake et al., 2004).\n\nArbuscular mycorrhizal fungi secrete glomalin that accumulates in soil, contributing substantial amounts of stable SOC (Leake et al., 2004). \n\nThe structural complexity of mycelial network pathways have only recently been discovered (Leake et al., 2004). \n\n\"Mycorrhizal networks can contribute to sustainability by increasing nutrient-use efficiency, reducing infections by root pathogens, and increasing soil-aggregate stability and soil physical properties\" (Leake et al., 2004). \n\nGenerally stated, MF hyphae carry carbohydrates from plants into soil regions far beyond the conventional rhizosphere and release exudates and other compounds to interact with soil microbiota (Leake et al., 2004). "},{"_id":"66c996cb48d5a85245000039","treeId":"641e9e3b83e7b085f200008f","seq":7395306,"position":3,"parentId":"67001bf51b17cd5e39000054","content":"#Allen 2006\n\nThe effects of mycorrhizal fungi on soil physical structure and water flow are poorly understood, as before now the focus has been on their ability for increasing nutrient uptake from soils (Allen, 2006). \n\nIndividual fungal hyphae may be 2-10 micrometers in diameter but can extends across many hectares, penetrating soil pores to increase pathways for water flow and conductivity (Allen, 2006). \n\nThere can be several kilometers of hyphae present in a single gram of soil (Allen, 2006). \n\nMycorrhizal fungi typically acquire 10-30% of the plant's net carbon fixation and turn it over to hyphae in hours to days (Allen, 2006). \n\nMycorrhizal fungi are best known for their ability to take up and transport nutrients to the host plant in exchange for the plant's C (Allen, 2006). \n\nAnnual, tilled croplands subject to intensive fertilization and herbicide application have lost or dramatically reduced mycorrhizal fungi, therefore the properties of water movement are changed in these environments (Allen, 2006). \n\nIt can take several years for a newly established perennial system to establish a developed network of mycorrhizal fungi (Allen, 2006). "},{"_id":"66f360226c36c33b08000047","treeId":"641e9e3b83e7b085f200008f","seq":7395308,"position":4,"parentId":"67001bf51b17cd5e39000054","content":"#Spaccini et al., 2002\n\nHumified SOC can have an average residence time of several hundreds of years (Spaccini et al., 2002).\n\nWe used to think humic substances were huge polymers, but now we understand that they are associations of small molecules held together by weak forces, and interact closely with organic compounds in the soil (Spaccini et al., 2002).\n\nOne experiment found that addition of humid acids to soil significantly increased organic carbon sequestration, and confirmed the association between fine soil textural fractions and organic matter in soils (Spaccini et al., 2002). \n\nSequestration of carbon into the humic pool protects it by mineralization from microbial degradation (Spaccini et al., 2002). "},{"_id":"66be1712d93604202a00002b","treeId":"641e9e3b83e7b085f200008f","seq":6825677,"position":0.875,"parentId":null,"content":"##Materials & Methods\n\n####Soil sample collection\n How we randomized it\n Bulk density collections\n Different depths & labels\n Air-dried, homogenized, sifted through 2mm sieve\n CN machine\n\n\n \n"},{"_id":"66f4a196998cca8e5000004d","treeId":"641e9e3b83e7b085f200008f","seq":6825641,"position":1,"parentId":"66be1712d93604202a00002b","content":"##Sampling\n\nWe took soil samples from two pastures that represented the high and low quality spectrum of the ranch. Pasture 1 had been grazed periodically for several decades, had been irrigated since `[ ] ??` and had limited traffic across of it. Pasture 2 had been eliminated from the grazing plan, but had been grazed periodically as needs changed. Pasture 2 was adjacent to the barn facility, and had an old silage cement bunker and a carport on it, so there has been considerably heavier vehicle traffic across the pasture. \n`Biological monitoring`\n\nThe transects were chosen in a part of the pasture that seemed qualitatively representative of the entire pasture. Transect tape was laid down for 200m, and the center of the testing site was chosen at 50m. The transect was marked with physical guidelines (i.e. positions of utility poles, fence posts, and other physical characteristics that were not likely to change), compass bearing, and latitude/longitude bearings. The transect was divided into a 10m plot with sampling sites every 1 sq m. \n\n`Describe more on how Donovan laid out the transect site`"},{"_id":"67357e7deec9284dd8000061","treeId":"641e9e3b83e7b085f200008f","seq":6895271,"position":1,"parentId":"66f4a196998cca8e5000004d","content":"###Different ways of direct measurement\n\nThere are two practical ways to measure or estimate SOC seq: directly by measuring changes in C pools or indirectly by measuring C fluxes. Spatial variability is the main concern that limits accuracy of direct measurements- to decrease variability, samples should be taken to different depths and avoid pastures with concentrated feces on the surface (Soussana et al., 2010).\n\nSOC accumulates over time in a non-linear fashion. Soussana et al estimates that converting cropland back to grassland for 20 years restores 18% of native C stocks in moist climates and 7% in temperate dry climates (Soussana et al., 2010).\n\nMany SOC studies focus on the 0-30cm soil strata, as most accumulation occurs in those layers, but lose can occur from deeper horizons (Soussana et al., 2010).\n\nDonovan lists 5 laboratory techniques to measure soil carbon directly from soil samples. These include elemental analysis by dry combustion, acid treatments, loss on ignition, carbon fractions, and soil respiration. Of these, elemental analysis by dry combustion is considered the most accurate that is likely to detect change in the organic carbon fraction but measures total soil carbon (inorganic and organic) (Donovan, 2013). "},{"_id":"674d08c83b6c0dac06000083","treeId":"641e9e3b83e7b085f200008f","seq":7395682,"position":1,"parentId":"67357e7deec9284dd8000061","content":"\n####Direct measurement\n\nSOC sequestration can be estimated by directly measuring changes in carbon pools or indirectly by measuring carbon fluxes (Soussana et al., 2010). Donovan lists 5 laboratory techniques to measure soil carbon directly from soil samples. These include elemental analysis by dry combustion, acid treatments, loss on ignition, carbon fractions, and soil respiration. Of these, elemental analysis by dry combustion is considered the most accurate that is likely to detect change in the organic carbon fraction but measures total soil carbon (inorganic and organic) (Donovan, 2013). Since large quantities of carbon are already present in the soil, sensitive methods are needed to detect small changes (Ellert et al., 2002). Most SOC studies focus on the 0-30 cm soil strata (Soussana et al., 2010) because of the traditional thought that sequestration is brought about from decomposing surface litter and roots. "},{"_id":"689ad670b9b112e2fe00008e","treeId":"641e9e3b83e7b085f200008f","seq":7461494,"position":1,"parentId":"674d08c83b6c0dac06000083","content":"#Materials&Methods\n\n**Measurements and sample sizing**\n\nSOC sequestration can be estimated by directly measuring changes in carbon pools or indirectly by measuring carbon fluxes (Soussana et al., 2010). Five common laboratory techniques to measure soil carbon from a soil sample include elemental analysis by dry combustion, acid treatments, loss on ignition, carbon fractions, and soil respiration (Donovan, 2013). Of these, elemental analysis by dry combustion is considered the most accurate that is likely to detect change in the organic carbon fraction but measures total soil carbon (inorganic and organic) (Donovan, 2013). Since large quantities of carbon are already present in the soil, sensitive methods are needed to detect small changes (Ellert et al., 2002). Most SOC studies focus on the 0-30 cm soil strata (Soussana et al., 2010) because of the traditional thought that sequestration is brought about from decomposing surface litter and roots. For our study, we took measurements from three horizontal strata: 0-10 cm, 10-25 cm, and 25-40 cm.\n\nCost and practicality are limiting factors when taking soil measurements, and for the purposes of this experiment we were limited to very few samples. However, Pringle et al found success with using 25 soil samples per unit to estimate baseline mean soil organic carbon to within 20% of the true mean to a depth of 30 cm (Pringle et al., 2011). A 2002 study found that six cores per microplot is adequate to represent a range of soil samples within more uniform sites (Conant et al., 2002). Sampling from different horizontal strata reduces variability since deeper layers have less spatiotemporal variation and can help to account for differences in soil types, vegetation cover, and management (Donovan, 2013). The power of testing microsites to make broad generalizations about an entire pasture is limited (Donovan, 2013), and taking samples from multiple microplots in the future will decrease variability (Conant et al., 2002).\nThe purpose of our experiment was to establish a baseline SOC pool in two separate pastures to compare future carbon changes, if any. The same microplots will be samples in the future to enhance statistical power (Conant et al., 2002). \n"},{"_id":"68a2408657c8c24e4800009a","treeId":"641e9e3b83e7b085f200008f","seq":7564022,"position":2,"parentId":"674d08c83b6c0dac06000083","content":"**Our study**\n\nWe took soil samples from two pastures that represented the high and low quality spectrum of the ranch. Pasture 1 had been grazed periodically for several decades, had been irrigated since [ ] ?? and had limited traffic across of it. Pasture 2 had been eliminated from the grazing plan, but had been grazed periodically as needs changed. Pasture 2 was adjacent to the barn facility, and had an old silage cement bunker and a carport on it, so there has been considerably heavier vehicle traffic across the pasture.\nBiological monitoring\nThe transects were chosen in a part of the pasture that seemed qualitatively representative of the entire pasture. Transect tape was laid down for 200m, and the center of the testing site was chosen at 50m. The transect was marked with physical guidelines (i.e. positions of utility poles, fence posts, and other physical characteristics that were not likely to change), compass bearing, and latitude/longitude bearings. The transect was divided into a 10m plot with sampling sites every 1 sq m.\n\nThe purpose of our experiment is to establish a baseline amount of soil organic carbon in two pastures to compare future data. We chose two pastures that are close in physical proximity but differ in the grazing management applied to them. Our hypothesis is that the two pastures will contain different quantities of soil organic carbon in the 0-10 cm strata due to their different grazing management, but similar quantities in the 10-25 cm and 25-40 cm strata because of their proximity and similar soil types. \n\nThe drylot pasture is located close to a riparian area and borders a barn which was a historic dairy. The pasture has a concrete silo for silage storage, and a large carport for storing tractors and machinery. Thus, the pasture has experienced more vehicle traffic than the irrigated pasture. The drylot pasture1 was largely left out of the planned grazing and used only when the sheep needed an overflow area for a day or two, so it has been grazed irregularly and overgrazed at times. It is not irrigated.\nThe irrigated pasture is located on the opposite side of the barn from Pasture 1 and also borders a riparian area. It is irrigated regularly during dry summer months, and has been grazed by sheep using holistically planned short-duration, high-intensity rotational grazing. It is usually grazed with a stocking density of 60-90 ewes during the winter, or up to 100 lambs during the summer, and grazed for a period of 7-10 days before getting 45-50 days of rest.\n\nWe collected soil samples in early December 2015 using a soil corer to take a 0-10 cm, 10-25 cm, and 25-40 cm sample from stratified simple random sites. See fig Donovan's picture for placement of soil samples. The samples were oven-dried and ground with mortar and pestle to homogenize them, then poured through a 2mm sieve to remove rock and root debris. The samples were run through a CN element analyzer `make and model`. \n"},{"_id":"673591afeec9284dd8000066","treeId":"641e9e3b83e7b085f200008f","seq":6895273,"position":2,"parentId":"66f4a196998cca8e5000004d","content":"###Sample Size\n\nPringle et al utilized linear mixed models to propose how grazing pressure and soil type affects SOC and stable carbon isotope ratio of SOC and explored the amount of soil sampling required to adequately determine baseline SOC. They found that soil type and grazing pressure interact to influence SOC to 30 cm depth. At 50 cm, there was no grazing effect but the soil type remained a significant factor. They recommended to cattle-grazing properties in tropical rangelands of Australia to divide properties into units of uniform soil type and grazing management, and use stratified simple random sampling to take 25 soil sampling locations about each unit, with at least 2 samples collected per soil stratum. They proposed that 25 soil samples per unit is adequate to estimate baseline mean SOC to within 20% of true mean to depth of 30 cm (Pringle et al., 2011).\n\nLarge quantities of carbon are already present in soils, so sensitive methods are needed to detect small changes in soil C storage (Ellert et al., 2002).\n\nQuantitative assessments of SOC are crucial to describe ecosystem function (Ellert et al., 2002).\n\nA 2002 study compared treatments in a randomized design that were treated with a known quantity of coal to compare the accuracy of soil sampling carbon measurements. The total C and N was analyzed using a CN analyzer, like our experiment. The “microsite approach” as the researchers called it, “successfully resolved small changes” in soil C storage relative to the much larger quantities already present. They did use bulk density corrections to correct for the differences in soil mass.\n\nA 2002 study found that six cores per microplot is “adequate” to represent a range of soil samples within more uniform sites: however, this method is not appropriate for all systems (Conant et al., 2002). They recommended that multiple microplots be sampled in the future to decrease variability.\n\nConant et al reommended to resample the same microplots for future measurements, as this enhances statistical power and allows changes to be detected years earlier (Conant et al., 2002).\n\nSampling from different horizontal strata reduces variability since deeper layers have less spatiotemporal variation and can help to account for differences in soil types, vegetation cover, management, etc. (Donovan, 2013).\nMASS OF CARBON: TOTAL CARBON = FRACTION CARBON (DECIMAL) X DENSITY X VOLUME IN CUBIC METERS\nSTANDARD ERROR= STANDARD DEVIATION OF ALL SAMPLES DIVIDED BY SQUARE ROOT OF NUMBER OF SOIL CORES\nTesting microsites to make broad conclusions about a pasture’s soil carbon content is analogous to comparing three tax returns in a small town to gain an accurate view of the average personal income (Donovan, 2013).\n\nThe minimum detectable difference is inversely related to the number of samples required (Conant et al., 2002)>"},{"_id":"6839a8162c07b5777d00008e","treeId":"641e9e3b83e7b085f200008f","seq":7395723,"position":1,"parentId":"673591afeec9284dd8000066","content":"####Sample size\n\nCost and practicality are limiting factors when taking soil measurements, and for the purposes of this experiment we were limited to very few samples (`XX in total`). However, Pringle et al found `success` with taking 25 soil samples per unit to estimate baseline mean soil organic carbon to within 20% of the true mean to a depth of 30 cm (Pringle et al., 2011). A 2002 study found that six cores per microplot is adequate to represent a range of soil samples within more uniform sites, however this strategy is limited to systems with more inherent spatiotemporal variability (Conant et al., 2002). Multiple microplots should be sampled to decrease variability (Conant et al., 2002). \n\nSampling from different horizontal strata reduces variability since deeper layers have less spatiotemporal variation and can help to account for differences in soil types, vegetation cover, and management (Donovan, 2013). The power of testing microsites to make broad generalizations about an entire pasture is limited (Donovan, 2013), and taking samples from multiple microplots in the future will decrease variability (Conant et al., 2002). \n\nThe purpose of our experiment was to establish a baseline SOC pool in two separate pastures to compare future carbon changes, if any. The same microplots will be samples in the future to enhance statistical power (Conant et al., 2002). "},{"_id":"66f4ae54998cca8e5000004e","treeId":"641e9e3b83e7b085f200008f","seq":6825674,"position":2,"parentId":"66be1712d93604202a00002b","content":"##Soil Cores\n\nSoil cores were taken with a manual core driver (Name??). Litter was scraped off of the surface with a dull knife and the corer was hammed into the soil. Samples were measured for core length with a tape measure, placed into bags, and air-dried. Bulk density samples were taken with a (??). \n\nThe samples were oven-dried for 24 hours and then removed. Samples were ground with a mortar and pestle to homogenize them, and poured through a 2mm sieve to remove much of the rock and debris that would skew results because of larger inorganic carbon content in rock fragments `source?`. \n\nHomogenized soil samples were run through a CN analyzer (`make and model`). "},{"_id":"6846e00e3b69a950f5000093","treeId":"641e9e3b83e7b085f200008f","seq":7403259,"position":1,"parentId":"66f4ae54998cca8e5000004e","content":"####Purpose of our experiment\n\nThe purpose of our experiment is to establish a baseline amount of soil organic carbon in two pastures to compare future measurements to. We chose two pastures that are close in physical proximity but differ in the grazing management applied to them. \n\n"},{"_id":"6846e0993b69a950f5000094","treeId":"641e9e3b83e7b085f200008f","seq":7403263,"position":2,"parentId":"66f4ae54998cca8e5000004e","content":"####Hypothesis\n\nOur hypothesis is that the two pastures have different quantities of soil organic carbon in the 0-10 cm strata due to their different grazing management, but similar quantities in the 10-25 cm and 25-40 cm strata because of their proximity and similar soil types. "},{"_id":"6846e0e43b69a950f5000095","treeId":"641e9e3b83e7b085f200008f","seq":7403349,"position":3,"parentId":"66f4ae54998cca8e5000004e","content":"####Description of Cheda Ranch & pastures\n\nPasture 1 is located close to a riparian area and borders a barn which was a dairy until the `??`. The pasture has a concrete silo for silage storage, and a large carport for storing tractors and machinery. Thus, the pasture has experienced more vehicle traffic than Pasture 2. Pasture 1 was largely left out of the planned grazing and used only when the sheep needed an overflow area for a day or two, so it has been grazed irregularly and overgrazed at times. It is not irrigated.\n\nPasture 2 is located on the opposite side of the barn from Pasture 1 and is about `__` meters away. It is irrigated regularly during dry summer months, and has been grazed by sheep using holistically planned intensive rotational grazing. It is typically heavily grazed once every 45-50 days and experiences minor, sporadic vehicular traffic."},{"_id":"689ff3280508bc74330000a7","treeId":"641e9e3b83e7b085f200008f","seq":7458558,"position":1,"parentId":"6846e0e43b69a950f5000095","content":"* Get GPS coordinates\n*Quantify high-intensity short-duration grazing -- stocking density, duration of grazing, rest period"},{"_id":"6846e24a3b69a950f5000096","treeId":"641e9e3b83e7b085f200008f","seq":7403427,"position":4,"parentId":"66f4ae54998cca8e5000004e","content":"####Soil sampling, processing, CN analyzer\n\nWe collected soil samples in early December 2015 using a soil corer to take a 0-10 cm, 10-25 cm, and 25-40 cm sample from stratified simple random sites `?`. See fig `Donovan's picture` for placement of soil samples. The samples were oven-dried and ground with mortar and pestle to homogenize them, then poured through a 2mm sieve to remove rock and root debris. The samples were `run through` a CN element analyzer `make and model`. \n"},{"_id":"68a0048a0508bc74330000a8","treeId":"641e9e3b83e7b085f200008f","seq":7458588,"position":1,"parentId":"6846e24a3b69a950f5000096","content":"* get ahold of Donovan \n* CN element analyzer make & model- or as footnote"},{"_id":"6846e2bf3b69a950f5000097","treeId":"641e9e3b83e7b085f200008f","seq":7403249,"position":5,"parentId":"66f4ae54998cca8e5000004e","content":"####Statistical analysis "},{"_id":"66f4b62f998cca8e5000004f","treeId":"641e9e3b83e7b085f200008f","seq":6825676,"position":3,"parentId":"66be1712d93604202a00002b","content":""},{"_id":"674cd0733b6c0dac0600007f","treeId":"641e9e3b83e7b085f200008f","seq":7113531,"position":4,"parentId":"66be1712d93604202a00002b","content":"###Soil survey\n\n[ ] what type of soil do we have? \n[ ] land classification\n[ ] organic matter characteristics- drainage, etc. "},{"_id":"674cd1c93b6c0dac06000081","treeId":"641e9e3b83e7b085f200008f","seq":7113536,"position":1,"parentId":"674cd0733b6c0dac0600007f","content":"http://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx"},{"_id":"68a008ed0508bc74330000a9","treeId":"641e9e3b83e7b085f200008f","seq":7458621,"position":1,"parentId":"674cd1c93b6c0dac06000081","content":"* soils that comprise majority of pasture\n* taxonomic description \n* depth of soil & of different horizons\n* soil texture\n* bulk density "},{"_id":"66be28d5d93604202a00002c","treeId":"641e9e3b83e7b085f200008f","seq":6825681,"position":0.9375,"parentId":null,"content":"##Results\n\n\n####Statistical analysis\n Bulk density\n Mass of C in pastures\n Mini tab\n Two-factor ANOVA\n 95% confidence interval\n Power analysis\n\n####Tables/Figures\n Soil survey map of pastures\n Samples and CI \n Power analysis?\n Raw data\n Equation for finding mass of carbon\n\n####Statistical analysis\n What we have found: in five years, we are confident that we will be able to monitor a change in carbon\n However: what is the change from? \n Plan to change management practices\n\n"},{"_id":"674cd8773b6c0dac06000082","treeId":"641e9e3b83e7b085f200008f","seq":7439054,"position":1,"parentId":"66be28d5d93604202a00002c","content":"###Statistical analysis\n\n\"individual value plot of C content %\"\nShows irrigated vs drylot pastures and strata A, B, C\n95% confidence level \nANOVA: p value of 0.865 for pastures, 0.114 for pasture by layer. \nalpha of 0.05\n\n\"Tukey pairwise comparisons\"\nat 95% confidence, difference in the means between ALL strata A, B, and C --\"significantly different\"\nindividual confidence level 98.01% \n\n\"Tukey pairwise comparisons pasture by layer\"\nBoth pastures had significantly differnet means in layer A than B and C, but B and C showed no statistical difference between them\n\n**figures to include**\nindividual value plot of C content\npower curve for general full factorial\nraw data from CN analyzer?"},{"_id":"68a0243d0508bc74330000aa","treeId":"641e9e3b83e7b085f200008f","seq":7458709,"position":1,"parentId":"674cd8773b6c0dac06000082","content":"Don't need to describe everything...\n* what we tested\n* what was significant in the test \n* significant what did and did not show a difference"},{"_id":"68a02a2c0508bc74330000ab","treeId":"641e9e3b83e7b085f200008f","seq":7458715,"position":2,"parentId":"674cd8773b6c0dac06000082","content":"Credit for stasticians...\n\nCover page and acknowledgements page "},{"_id":"68a1f73646884844210000ad","treeId":"641e9e3b83e7b085f200008f","seq":7563987,"position":1,"parentId":"68a02a2c0508bc74330000ab","content":"#Results\n\n**Experimental Results**\n\nWe looked at three comparing three variables analyzed during this experiment: comparison between pastures, strata, and pasture by strata. We used an alpha of 0.05 to detect small changes, and found no significant difference between the pastures (p=0.865), and no significant difference between pasture by strata (p=0.114). We found a significant difference between strata (p=0.000) as was expected due to the large amount of soil organic matter residing in the topsoil. The mean of the 0-10 cm, 10-25 cm, and 25-40 cm layer were significantly different from each other (3.07875, 1.88863, and 1.42988 respectively). We completed a power curve for general full factorial, and found that with 8 samples taken from the 0-10 cm layer, we had close to 100% power of detecting a 0.4 percent change in carbon. This is especially useful to land managers who wish to implement a small-scale carbon monitoring program without inputting costly equipment and labor to take research-scale sample sizes. "},{"_id":"68a02cc00508bc74330000ac","treeId":"641e9e3b83e7b085f200008f","seq":7458724,"position":3,"parentId":"674cd8773b6c0dac06000082","content":"Biological monitoring\n\n* put in introduction when describing the site \n* put table in Appendice if have data"},{"_id":"66f4b813998cca8e50000050","treeId":"641e9e3b83e7b085f200008f","seq":6835715,"position":0.953125,"parentId":null,"content":"##Discussion\n\n###Direct vs indirect methods of sampling\n\n###How many samples are needed \n\n###Spatiotemporal variability and randomized sampling\n\n###We don't know how management cahnges SOC but we will be able to tell if it changed\n###Importnat to find a practical methology for future establishments in carbon markets"},{"_id":"67001dda1b17cd5e39000055","treeId":"641e9e3b83e7b085f200008f","seq":6835687,"position":1,"parentId":"66f4b813998cca8e50000050","content":"####Comparison\n\nHow many samples are considered significant\nWhat our power and CI levels mean for baseline testing\nIn 5 years, we need to: \n"},{"_id":"673588aeeec9284dd8000065","treeId":"641e9e3b83e7b085f200008f","seq":6895230,"position":0.5,"parentId":"67001dda1b17cd5e39000055","content":"###How grazing affects C seq\n\nSoussana et al conducted a meta-analysis of 115 studies in pastures and grazing land. They found that improved management increased SOC levels in 74% of the studies. Improved management practices included fertilization, grazing management, conversion from cultivation, and improved grass species (Soussana et al., 2010).\n\nAn analysis of 115 studies in pastures found that light grazing increased SOC more than exclosure and heavy grazing (Soussana et al., 2010). However, the article did not specify whether the heavily grazed pastures were on a continuous or rotational grazing system.\n\n\nA crucial foundation in any system aiming to increasing SOC retention is to establish ground cover. Permanent soil cover quickly stabilizes water retention and reduces quantities of sediments, nutrients, and agricultural chemicals transported to surface waters within a few years (Whalen et al., 2003).\n\nEXPERIMENT: A study in the Great Plains chose 3 sites that represented 3 climactic gradients and cultivated native rangelands. In each site, plots were abandoned, seeded with non-native perennial grasses to establish permanent cover, or converted to annual crop production. Samples were obtained from 0-15 cm in depth. The soil bulk density was lower in the undisturbed native rangeland than modified plant communities, and the total C, N, and P contents declined with cultivation. The authors called for a need to collect deeper samples to determine if net gains or losses had occurred throughout the soil profile or were concentrated in the topsoil. The authors found that establishment of perennial grasses or legumes on formerly cultivated land could slow or reverse depletion of SOC, and stabilization or loss of C and N from modified plant communities is affected by climate as well as quantity and chemical characteristics of residues produced by plants (Whalen et al., 2003).\n\nLittle is known about how cattle grazing affects SOC (Pringle et al., 2011).\n\nThe substantial area of the globe devoted to grazing means that minor changes in SOC can cause proportionately large changes in C seq worldwide (Pringle et al, 2011).\n\nA 2010 global literature review found that SOC changed under contrasted grazing conditions across climactic gradients, and that the factors that control SOC in a grazed ecosystem are more complex than we currently think they are. General patterns that the study noted were that root contents, the primary control of SOC formation, were higher in grazer than ungrazed systems at the most arid and most tropical sites but were lower at temperate sites. The increased root biomass should increase SOC because of greater C inputs to the soils (Pineiro et al., 2010).\n\nGrazing can change how carbon allocates in the soil. Belowground biomass enters the soil directly and contributes more to soil organic matter formation than aboveground productivity. Grazing changes the proportion of NPP allocated to aboveground or belowground organs (Pineiro et al., 2010).\n\nOne researcher argues that grazing can affect NPP indirectly by altering species composition or soil resources by decreasing water availability (Pineiro et al., 2010).\n\n“Grazing animals, plants, soil biota and soils have co-evolved for over 20 million years, resulting in highly complex and sensitive inter-relationships” (Jones, 2006).\n\nA proposed method for how grazing soil carbon is how the plant readjusts for biomass loss after grazing. More carbon is contained in the roots than the leaves of the plant, and when the leaves are removed by grazing, and plant responds by readjusting its biomass balance. Some carbon is mobilized to the crown for production of new leaves, some is lost to the soil as root decomposition, and some is actively exuded into the rhizosphere. Thus, each grazing event becomes a “carbon injection” opportunity (Jones, 2008).\n\nPlants that are grazed continuously have poorly developed root systems and little C available for exudation into the soil (Jones, 2006).\n\n"},{"_id":"689ae6a4b9b112e2fe000090","treeId":"641e9e3b83e7b085f200008f","seq":7452656,"position":0.5,"parentId":"673588aeeec9284dd8000065","content":"Small changes in carbon pools have drastic effects in the global climate system (Schlesinger, 1995).\nLosses in soil organic matter can exacerbate global warming, but increases in soil organic matter can slow the rate of atmospheric CO2 release and “provide a negative feedback” to global warming (Schlesinger, 1995)."},{"_id":"6839b8d62c07b5777d00008f","treeId":"641e9e3b83e7b085f200008f","seq":7439071,"position":1,"parentId":"673588aeeec9284dd8000065","content":"####Grazing affects on SOC seq\n\nThe impact that soil carbon sequestration might have on global soils is effectively useless if the rates of sequestration or emissions cannot be manipulated by human management. For the purposes of this experiment, we are focusing on grazing land. The substantial area of the globe utilized for grazing means that small changes in SOC can cause proportionately large changes in global carbon sequestration (Pringle et al., 2011). However, little is currently known about how cattle grazing affects SOC (Pringle et al., 2011).\n\nA 2010 global literature review found that SOC changed under contrasted grazing conditions across climactic gradients, and that the factors that control SOC in a grazed ecosystem are more complex than we currently think they are. General patterns that the study noted were that root contents, the primary control of SOC formation, were higher in grazer than ungrazed systems at the most arid and most tropical sites but were lower at temperate sites. The increased root biomass should increase SOC because of greater C inputs to the soils (Pineiro et al., 2010). An analysis of 115 studies in pastures found that light grazing increased SOC more than exclosure and heavy grazing (Soussana et al., 2010). However, the article did not specify whether the heavily grazed pastures were on a continuous or rotational grazing system. One researcher argues that grazing can affect NPP indirectly by altering species composition or soil resources by decreasing water availability (Pineiro et al., 2010). Studies have found that SOC increases, decreases, or is relatively maintained in different grazing systems across climatic gradients, and the future `question` will be to describe exactly how grazing management manipulates the rate of carbon sequestration. \n\nGrazing is inherently difficult to describe in an experimental system because of the many different ways to graze pastures, the type of pasture that is being grazing, and abiotic climatic factors that affect the way grazing is conducted, as well as the different animals that graze in different ways and hence exert different affects on the aboveground and belowground communities. Christine Jones writes elegantly, \"Grazing animals, plants, soil biota and soils have co-evolved for over 20 million years, resulting in highly complex and sensitive inter-relationships\" (Jones, 2006). There is no universal way to describe how grazing affects soil carbon sequestration, but the attempts are to broadly describe affects that should either entice or discourage producers from making changes that could enhance or stop soil carbon sequestration.\n\nOne very simple proposed method for how grazing soil carbon is how the plant readjusts for biomass loss after grazing. More carbon is contained in the roots than the leaves of the plant, and when the leaves are removed by grazing, and plant responds by readjusting its biomass balance. Some carbon is mobilized to the crown for production of new leaves, some is lost to the soil as root decomposition, and some is actively exuded into the rhizosphere. Thus, each grazing event becomes a “carbon injection” opportunity (Jones, 2008). However, much more research is indicated to examine different grazing management systems and their affects on soil microbial communities such as arbuscular mycorrhizal fungi, that will in turn affect rates of carbon sequestration. In addition, the best way to compile data on different management systems is to educate and encourage producers to start their own carbon monitoring practices that can be compiled into open-source data networks, much like the Soil Carbon Coalition, a non-profit organization dedicated to sharing open-source data between producers (Donovan, 2015). \n\nWe propose that in the ensuing five years, the amount of carbon contained in our pastures will change based on the grazing management applied to the pastures. In December 2015, both pastures were seeded with a no-till seeded with a cover crop cocktail of `??`. The drylot pasture was incorporated into the grazing plan and will experience the same short-duration, high-intensity rotational grazing that the irrigated pasture is managed with, but with a smaller duration of time. We hypothesize that in five years, the carbon content of the drylot pasture will have increased in the A strata, and will likely increase in the B and C layer due to better-developed root systems that can partner with mycorrhizal fungi to channel carbon deeper into the soil profile. If grazing management, irrigation management, and soil disturbances are well managed, there should be an increase of carbon in the irrigated pasture as well. If management stays approximately the same, the carbon content in the irrigated pasture should reflect only natural fluxes. "},{"_id":"689ae006b9b112e2fe00008f","treeId":"641e9e3b83e7b085f200008f","seq":7452661,"position":1,"parentId":"6839b8d62c07b5777d00008f","content":"#Discussion\n\n**Grazing effects on soil carbon sequestration**\n\nThe impact that soil carbon sequestration might have on global soils is effectively useless if the rate of sequestration cannot be manipulated by human management. Luckily, the immense size of the global soil pool means that small changes in carbon pools can have drastic effects on the global climate system (Schlesinger, 1995). The substantial area of the globe utilized for grazing means that small changes in SOC can cause proportionately large changes in global carbon sequestration (Pringle et al., 2011). In California, grazing land makes up approximately half of land use (Silver et al., 2010). However, little is currently known about how cattle grazing affects SOC (Pringle et al., 2011).\nA 2010 global literature review found that SOC changed under contrasted grazing conditions across climactic gradients, and that the factors that control SOC in a grazed ecosystem are more complex than previously thought. General patterns that the study noted were that root contents were higher in grazer than ungrazed systems at the most arid and most tropical sites but were lower at temperate sites, and thought to increase soil carbon by increasing biomass decomposition (Pineiro et al., 2010). An analysis of 115 studies in pastures found that \"light grazing\" increased SOC more than exclosure and \"heavy grazing\" (Soussana et al., 2010). However, the article did not specify whether the heavily grazed pastures were on a continuous or rotational grazing system, or how the stocking density related to the carrying capacity of the specific pastures. Studies have found that SOC increases, decreases, or is relatively maintained in different grazing systems across climatic gradients, and the challenge is to understand the relationship between grazing management and soil carbon sequestration.\nGrazing is inherently difficult to describe in an experimental system because of the many different ways to graze pastures, the type of pasture that is being grazing, and abiotic climatic factors that affect the way grazing is conducted, as well as behavioral characteristics of grazing herbivore that affect aboveground and belowground communities. Jones states, \"grazing animals, plants, soil biota and soils have co-evolved for over 20 million years, resulting in highly complex and sensitive inter-relationships” (Jones, 2006). There is no universal way to describe how grazing affects soil carbon sequestration, but the attempts are to broadly describe effects that should incentive producers to make changes that will enhance soil carbon sequestration rates. \nOne very simple proposed method for how grazing soil carbon is how the plant readjusts for biomass loss after grazing. More carbon is contained in the roots than the leaves of the plant, and when the leaves are removed by grazing, and plant responds by readjusting its biomass balance. Some carbon is mobilized to the crown for production of new leaves, some is lost to the soil as root decomposition, and some is actively exuded into the rhizosphere. Thus, each grazing event becomes a “carbon injection” opportunity (Jones, 2008). However, much more research is indicated to examine different grazing management systems and their effects on soil microbial communities such as arbuscular mycorrhizal fungi. An efficient strategy to compile data is to educate and encourage producers to start their own carbon monitoring practices that can be compiled into open-source data networks, much like the Soil Carbon Coalition, a non-profit organization dedicated to sharing open-source data between producers (Donovan, 2015).\nWe propose that in the ensuing five years, the amount of carbon contained in our pastures will change due to the grazing management applied to the pastures. The drylot pasture was incorporated into the grazing plan and will experience the same short-duration, high-intensity rotational grazing that the irrigated pasture is managed with, but with a smaller duration of time. We hypothesize that in five years, the carbon content of the drylot pasture will have increased in the 0-10 cm strata, and will likely increase in the 10-25 cm and 25-40 cm horizons due to more developed root systems whose relationship with mycorrhizal fungi channels carbon deeper into the soil profile. If grazing management, irrigation management, and soil disturbances are well managed, there should be an increase of carbon in the irrigated pasture as well. If management stays approximately the same, the carbon content in the irrigated pasture should reflect only natural fluxes.\n"},{"_id":"689b0071b9b112e2fe000091","treeId":"641e9e3b83e7b085f200008f","seq":7452677,"position":2,"parentId":"6839b8d62c07b5777d00008f","content":"#Discussion\n\n**Best Management Practices**\n\nRecent studies have suggested that making changes in land management can improve the rates of soil carbon sequestration. Soussana et al conducted a meta-analysis of 115 studies in pastures and grazing land and found that improved management increased SOC levels in 74% of the studies. Improved management practices included fertilization, grazing management, conversion from cultivation, and improved grass species (Soussana et al., 2010). However, little has been studied about the relationships between climate, stocking rates, grazing systems, and carbon dynamics (Fynn et al., 2010), and conventional grazing studies focus almost exclusively on continuous grazing systems. Some broadly drawn recommendations have been made, most originating from practices that have been solidly shown to improve factors that lead to improve soil carbon sequestration. In semi-arid grasslands, producers should reduce burning, control stocking rates, and improve nitrogen dynamics by avoiding excessive nitrogen inputs (Batjes 1998; Pineiro et al., 2010). \nChanging management practices to those that shift the soil biochemical environment to favor fungi can reduce the rates of SOC decomposition and enhance sequestration (Jones, 2008). Practices that show potential for accomplishing this include planting perennial species, reducing tillage, maintaining neutral soil pH, ensuring adequate drainage, and minimizing erosion (Jastrow et al., 2007).\nGeneral grazing system management changes emerging in the realm of sustainability research show promise to improve soil carbon sequestration as well. These include adjustments in stocking rates, introduction of grasses on degraded lands, managing invasive species, reseeding grassland species, riparian zone restoration, and introduction of biochar to soils (Fynn et al., 2010). Our study will contribute longitudinal data on rotational grazing systems, which have not been studied in depth. \nAn indirect method to improve soil carbon sequestration is to avoid the loss of soil organic carbon through soil disturbance. SOC loss is exaggerated in agricultural ecosystems with severe soil degradation (Lal, 2004) and especially exacerbated in dry and warm climates (Lal et al., 1995). Carbon loss from soils is emitted directly into the atmosphere and reduces soil quality and biomass productivity, and negatively impacts water quality (Lal, 2004). \n"},{"_id":"67357f55eec9284dd8000062","treeId":"641e9e3b83e7b085f200008f","seq":6895312,"position":1,"parentId":"67001dda1b17cd5e39000055","content":"###Management recommendations\n\nSoussana et al made four recommendations in their 2004 study. The authors recommended reducing N fertilizer inputs in highly intensive grasslands, increasing duration of grass fallows, convert fallows to grass-legume mixtures or permanent grasslands, and moderately intensifying nutrient-poor permanent grasslands (Soussana et al., 2004).\n\nThe challenge in determining how management practices affect soil carbon sequestration lies in determining the relationships among precipitation, stocking rate, and carbon dynamics (Fynn et al., 2010).\n\nPractices that Batjes recommends to enhance soil C seq are to account for different soil types, suitability, and factors for soil formation before cultivating or grazing land. Semi-arid grassland management can focus on reduction of burning, improving the soil nutrient status, and introducing improved grasses and legumes in combination with controlled stocking rates (Batjes 1998).\n\nMore efficient Nitrogen conservation can affect SOC stocks, according to Pineiro et al. The authors recommended avoiding “unwanted” N emissions from excessively loading grazing systems with nitrogen inputs, and that N dynamics would allow increased C seq in soils, and increased soil fertility (Pineiro et al., 2010).\n\nDr. Rattan Lal recommends these strategies to increase SOC: soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands (Lal, 2004).\n\nSOC loss is exaggerated in agricultural ecosystems with severe soil degradation. Carbon loss from soils is emitted directly into the atmosphere and reduces soil quality and biomass productivity, and negatively impacts water quality (Lal, 2004).\n\nManagement practices that are recommended by Lal add biomass to the soil, cause minimal soil disturbance, improve soil structure, enhance soil microbiota biodiversity, and strengthen mechanisms of nutrient and water cycling (Lal, 2004).\n\n“Long term enhancement of SOC seq requires sustained primary productivity and efficient feedback between communities of plants and soil biota for carbon and nutrient cycling” (De Deyn et al., 2008).\n\nMaximizing the balance between soil carbon input and output is the best way to enhance SOC seq (De Deyn et al., 2008).\n\nChanging management practices to those that shift the soil biochemical environment to favor fungi can reduce the rates of SOC decomposition and enhance sequestration. Practices that show potential for accomplishing this include planting perennial species, reducing tillage, maintaining neutral soil pH, ensuring adequate drainage, and minimizing erosion (Jastrow et al., 2007).\n\nManagement recommendations made by Flynn et al for increased carbon sequestration include adjustments in stocking rates, introduction of grasses on degraded lands, managing invasive species, reseeding grassland species, riparian zone restoration, and introduction of biochar to soils (Fynn et al., 2010)."},{"_id":"6839daed2c07b5777d000090","treeId":"641e9e3b83e7b085f200008f","seq":7395808,"position":1,"parentId":"67357f55eec9284dd8000062","content":"####Management Recommendations\n\nRecent studies have suggested that making changes in land management, some minor and some drastic, can improve the rates of soil carbon sequestration. Soussana et al conducted a meta-analysis of 115 studies in pastures and grazing land. They found that improved management increased SOC levels in 74% of the studies. Improved management practices included fertilization, grazing management, conversion from cultivation, and improved grass species (Soussana et al., 2010). The challenge in determining how management practices affect soil carbon sequestration lies in teasing apart the relationships between climate, stocking rates, grazing systems, and carbon dynamics (Fynn et al., 2010). Some broadly drawn recommendations have been made, most stemming from factors that have been solidly shown to improve factors that lead to improve soil carbon sequestration. In semi-arid grasslands, producers should reduce burning, control stocking rates, and improve nitrogen dynamics by avoiding excessive nitrogen inputs (Batjes 1998, Pineiro et al., 2010).\n\nChanging management practices to those that shift the soil biochemical environment to favor fungi can reduce the rates of SOC decomposition and enhance sequestration. Practices that show potential for accomplishing this include planting perennial species, reducing tillage, maintaining neutral soil pH, ensuring adequate drainage, and minimizing erosion (Jastrow et al., 2007).\n\nGeneral grazing system management changes emerging in the realm of sustainability research show promise to improve soil carbon sequestration as well. These include adjustments in stocking rates, introduction of grasses on degraded lands, managing invasive species, reseeding grassland species, riparian zone restoration, and introduction of biochar to soils (Fynn et al., 2010). \n\nAn indirect way to improve soil carbon sequestration is to avoid the loss of soil organic carbon through soil disturbance. SOC loss is exaggerated in agricultural ecosystems with severe soil degradation. Carbon loss from soils is emitted directly into the atmosphere and reduces soil quality and biomass productivity, and negatively impacts water quality (Lal, 2004).\n\n\n"},{"_id":"66be2b7bd93604202a00002d","treeId":"641e9e3b83e7b085f200008f","seq":6783931,"position":0.96875,"parentId":null,"content":"##Conclusion\n\n####What this research means\n Compared to literature\n Soil Carbon Coalition\n####Call for further research\n Need to do this study on a larger scale\n Encourage producers to establish their own baesline data\n Preparation for a carbon market?"},{"_id":"67358461eec9284dd8000063","treeId":"641e9e3b83e7b085f200008f","seq":6894535,"position":1,"parentId":"66be2b7bd93604202a00002d","content":""},{"_id":"67359f03eec9284dd8000067","treeId":"641e9e3b83e7b085f200008f","seq":7395809,"position":0.5,"parentId":"67358461eec9284dd8000063","content":"###Carbon Markets\n\nCarbon markets have been in use since 2002, mostly in European Union countries. The “commodification of soil C is important for trading C credits” (Lal, 2004).\n\nThe basic idea of a “carbon market” is to instill a financial incentive to producers to sequester soil organic carbon on their land. Increased soil carbon levels would be converted to verified emissions reductions to use within an offset market, cap and trade system, or other credit program (Fynn et al., 2010).\n\nIn terms of sampling, accuracy costs more and cheaper methods are traditionally less accurate (Fynn et al., 2010).\n\n“Rather than tie a protocol to the limitations of one particular method, it is logical to combine the strengths of different methods into a single methodology, which may be updated as economics and technical advances allow” (fynn et al., 2010).\n\n#Lara et al., nd\nQuantifying “ecosystem services” is a complex and convoluted process, albeit necessary to quantify the value to human societies that natural capital resources bring. Modern agriculture is a “major driver of global environment change” and there are numerous efforts to establish sophisticated economic models to predict global effects of carbon sequestration efforts. These include ARIES (artificial intelligence for ecosystem services) which takes open source data into account, InVEST (integrated valuation of ecosystem services and tradeoffs) which provides maps of monetary value among other outputs, and MAgPIE (Model of agricultural production and its impact on the environment) which shows potential output of carbon storage in soils and crop residue, etc (Lara et al, nd). These are just a few of numerous modeling systems that could be of future use towards establishing a global or domestic carbon market."},{"_id":"6839fda0bafcb1d7ac00007d","treeId":"641e9e3b83e7b085f200008f","seq":7395813,"position":1,"parentId":"67359f03eec9284dd8000067","content":"####Carbon markets\n\nCarbon markets are an economically crucial conversation to have whenever discussing soil carbon sequestrations. The basic idea of a “carbon market” is to instill a financial incentive to producers to sequester soil organic carbon on their land. Increased soil carbon levels would be converted to verified emissions reductions to use within an offset market, cap and trade system, or other credit program (Fynn et al., 2010). Carbon markets have been in use since 2002, mostly in European Union countries (Lal, 2004). Quantifying “ecosystem services” is a complex and convoluted process, albeit necessary to quantify the value to human societies that natural capital resources bring (Lara et al., nd). There have already been numerous efforts to establish economic models to predict global effects of carbon sequestration efforts (Lara et al., nd). While these are largely out of the scope of this paper, it is important that to mention that the more we know about the relationships of carbon sequestration and grazing practices, the closer we can get to establishing carbon markets that provide incentive to producers to make changes that will simultaneously mitigate climate change. \n\n "},{"_id":"689b2413b9b112e2fe000092","treeId":"641e9e3b83e7b085f200008f","seq":7452683,"position":1,"parentId":"6839fda0bafcb1d7ac00007d","content":"#Conclusion\n\n**Implications for carbon markets**\n\nCarbon markets are an economically valid proposal to incentive the agricultural segment to reduce greenhouse gas emissions, soil carbon emissions, and to improve soil carbon sequestration on private and public land. The basic idea of a carbon market is to instill a financial incentive to producers to sequester soil organic carbon on their land. Increased soil carbon levels would be converted to verified emissions reductions to use within an offset market, cap and trade system, or other credit program (Fynn et al., 2010). Carbon markets have been in use since 2002, mostly in European Union countries (Lal, 2004). Quantifying “ecosystem services” is a complex and convoluted process, albeit necessary to quantify the value to human societies that natural capital resources bring (Lara et al., nd). It is important that to mention that the more we know about the relationships of carbon sequestration and grazing practices, the closer we move towards establishing carbon markets that provide incentive to producers to make changes that will simultaneously mitigate climate change.\n\n**Conclusion**\n\nThe purpose of this study is to examine an economically viable, low-labor method to establish a baseline soil organic carbon pool while collecting baseline data for longitudinal analysis. We found that there were significant differences in SOC content between two pastures that are in close proximity but have been under differing grazing management, and that our small soil sample number of 32 total samples gives sufficient confidence to detect changes in the SOC pool, while sampling from different strata increases the chance of detecting change related to management changes. This is encouraging to land managers and producers who wish to establish their own carbon monitoring systems without the use of much funding or infrastructure in preparation for the establishment of a formal carbon market. More research is indicated to establish greater accuracy in a greater number of microsites, and increased core samples within microsites.\nThere has been an explosive, global increase in focus on carbon sequestration. In December 2015, France unveiled its 4% Initiative, which is is a voluntary group of stakeholders committed to action plans that implement management practices to enhance the soil organic pool of France’s soils. The initiative’s plan of action included structuring for multipartner action programs to better manage for soil carbon, and funding for international research and scientific cooperation programs (Ministry of Agriculture, 2015). Generally, the recommended management practices to improve soil carbon are natural, cost-effective, and environmentally-friendly (Lal, 2004). While more governments and agricultural programs are becoming open to the idea of carbon sequestration as a viable way to restore degraded agricultural lands, more research is called for to better understand the relationships between agricultural systems and carbon dynamics. The scientific community needs to be open to new pathways of carbon flow, as we discover more about soil microbiota and their ecosystems (De Deyn et al., 2008). Producers should begin to implement their own carbon monitoring methods, both in preparation for impending carbon market systems and in tandem with soil improvement strategies. The research techniques delineated in Donovan’s “Measuring Soil Change” are low-cost strategies that producers can use with their own equipment and very little money to analyze soil carbon content with statistical validity (Donovan, 2013). Open-source data from individual producers could aid greatly in understanding the relationships between management changes and soil carbon pools, as there is a lack of published data from California in particular, namely in areas that are not in close proximity to agricultural research stations (Silver et al., 2010). There should be further research in establishing economically viable and statistically significant techniques to link land management to changes in soil carbon pools to better understand the effect of soil health on carbon sequestration, and carbon sequestration on soil health.\n\n\n\n"},{"_id":"6735847deec9284dd8000064","treeId":"641e9e3b83e7b085f200008f","seq":6895259,"position":1,"parentId":"67358461eec9284dd8000063","content":"###Conclusion\n\n“The role of agriculture in sequestering of organic C by soils remains ambiguous. The overall picture is complicated by technological, social, economical and cultural factors” (Batjes 1998).\n\nCarbon sequestration is a bridge between 3 global issues: climate change, desertification, and biodiversity (Lal, 2004). Regardless of the climate change debate, it is a crucial issue that could increase productivity and water quality and restore degraded ecosystems (Lal, 2004).\n\nAgriculturally developing nations, especially those in tropical climates where dynamic soil processes exacerbate rates of SOC accumulation or loss, have the greatest need for change. Currently, the C sink capacity is high, but the rate of C seq is low and complicated by limited infrastructure and resource-poor agricultural systems (Lal, 2004).\n\nGenerally, soil C seq by adapting recommended management practices is a natural, cost-effective, and environmentally-friendly process (Lal, 2004).\n\nThe scientific community needs to be open to new plant traits and pathways of carbon flow, as we discover more about soil microbiota and their ecosystems (De Deyn et al., 2008)."},{"_id":"683a06acbafcb1d7ac00007e","treeId":"641e9e3b83e7b085f200008f","seq":7439089,"position":4,"parentId":"6735847deec9284dd8000064","content":"####Conclusion\n\nThe purpose of this research was to `test` an economically viable, low-labor method to establish a baseline soil organic carbon pool to make future comparisons to in five years. We found that there were significant differences in SOC content between two pastures that are in close proximity but have been under differing grazing management, and that our soil sample number [ ] ?? gave sufficient confidence to detect changes in years to come. This is encouraging to land managers and producers who wish to establish their own carbon monitoring systems without the use of much funding or `infrastructure` in preparation for the establishment of a formal carbon market. More research is indicated to establish the increments of accuracy that are found at greater numbers of microsites tested, and increased core samples within microsites. \n\nThere has been an increase in focus on carbon sequestration. In December 2015, France unveiled its 4% Initiative, which is is a voluntary group of stakeholders committed to action plans that implement management practices to enhance the soil organic pool of France’s soils. The initiative's plan of action included structuring for multipartner action programs to better manage for soil carbon, and funding for international research and scientific cooperation programs (Ministry of Agriculture, 2015). Generally, the recommended management practices to improve soil carbon are natural, cost-effective, and environmentally-friendly (Lal, 2004). While more governments and agricultural programs are becoming open to the idea of carbon sequestration as a viable way to restore degraded agricultural lands, more research is called for to better understand the relationships between agricultural systems and carbon dynamics. The scientific community needs to be open to new pathways of carbon flow, as we discover more about soil microbiota and their ecosystems (De Deyn et al., 2008). Producers should begin to implement their own carbon monitoring methods, both in preparation for impending carbon market systems and in tandem with soil improvement strategies. The research techniques delineated in Donovan's \"Measuring Soil Change\" are low-cost strategies that producers can use with their own equipment and very little money to analyze soil carbon content with statistical validity. Open-source data from individual producers could aid greatly in understanding the relationships between management changes and soil carbon pools, as there is a lack of published data from California in particular, namely in areas that are not in close proximity to agricultural research stations (Silver et al., 2010). There should be further research in establishing economically viable and statistically significant techniques to link land management to changes in soil carbon pools to better understand the effect of soil health on carbon sequestration, and carbon sequestration on soil health. "},{"_id":"66f39f0e6c36c33b0800004c","treeId":"641e9e3b83e7b085f200008f","seq":7395829,"position":2,"parentId":"67358461eec9284dd8000063","content":"#Bland 2015\n\nThe Lima-Paris Action Agenda, unveiled at the United Nation Climate Change Conference in November 2015, announced that the carbon farming movement is \"moving forwards\". Targeting the Action Agenda's goal of resilient societies with low carbon levels, it stated that a \"growing\" number of advocates say that \"one of the best opportunities for drawing carbon back to Earth is for its land managers to sequester more carbon in the soil\" (Bland, 2015).\n#Ministry of Ag, 2015\n\nIn December 2015, France unveiled its new 4% Initiative, which is a voluntary group of stakeholders committed to action plans that implement management practices to enhance the soil organic pool of France's soils. The initiative's plan of action included structuring for multipartner action programs to better manage for soil carbon, and funding for international research and scientific cooperation programs. The plan's title comes from a powerful hypothesis that a 4% annual growth rate of soil organic carbon stock would stop the present increase in atmospheric CO2.\n#Porter et al, 2014\n\nThe response of pastures to climate change is complex because it is riddled with indirect interactions of plant, soil, and atmospheric interactions at the biogeochemical level (Porter et al., 2014). \n\nIncreasing vegetative cover reduces soil erosion and loss of nutrients, increases soil carbon and resists temperature extremes (Porter at al., 2014)."},{"_id":"66f34ea26c36c33b08000045","treeId":"641e9e3b83e7b085f200008f","seq":7395825,"position":0.99999,"parentId":"66f39f0e6c36c33b0800004c","content":"#UNLPAA 2015\n\nPress release from Lima-Paris Action Agenda\n\nThe Lima-Paris Action Agenda, a joint undertaking of Peruvian and French presidencies, the Office of the Secretary-General of the UN and the UNFCCC Secretariat, met in December 2015 to cement action plans to tackle the global issue of climate change. They focused in on 6 major initiatives that support farmers, including France's 4% Initiative; Live Beef Carbon, a European cooperative to reduce the carbon footprint of the livestock sector; Adaptation for Smallholder Ag Program, investing climate finance for developing countries; and the Agro-ecology funding for West African countries, among more (UN LPAA, 2015). "},{"_id":"641e9e5483e7b085f2000091","treeId":"641e9e3b83e7b085f200008f","seq":6279556,"position":1,"parentId":null,"content":"# Literature Cited"},{"_id":"689a8b8cb9b112e2fe00008a","treeId":"641e9e3b83e7b085f200008f","seq":7452608,"position":17.25,"parentId":"641e9e5483e7b085f2000091","content":"Lal R., J. Kimble, E. Levine, C. Whitman. 1995. World soils and greenhouse effect: an overview. In: R. Lal, J. Kimble, E. Levine, B.A. Stewart, editors, Soils and global change. CRC Press, Boca Raton, FL. p. 1-8.\n\n#Lal1995\n\nThe atmospheric sink and marine sink leave an additional 1.8 Pg C/yr unaccounted for, believed to \"be absorbed by terrestrial ecosystems\" (Lal et al., 1995). \n\nThere are four pools of carbon on Earth: oceans, the atmosphere, terrestrial ecosystems, and geological formations (Lal et al., 1995). \n\nSoil degradation \"caused by land misuse, ecologically incompatible farming systems, and inappropriate soil management practices, can be a major cause of fertility depletion and gaseous emissions from soil\" (Lal et al., 1995). \n\nSoil degradation and desertification are critical problems in arid climate (Lal et al., 1995). \n\n\"Science-based, economically profitable, and ecologically-sustainable agricultural systems are soil-restorative and likely to sequester carbon in world soils\" (Lal et al., 1995). \n\nUncertainties in data assessment \"arise from unstandardized methods, data quality and reliability, and missing and incomplete data\" "},{"_id":"689a9e60b9b112e2fe00008b","treeId":"641e9e3b83e7b085f200008f","seq":7452610,"position":17.375,"parentId":"641e9e5483e7b085f2000091","content":"Schlesinger, W.H. 1995. An overview of the carbon cycle. In: R. Lal, J. Kimble, E. Levine, B.A. Stewart, editors, Soils and global change. CRC Press, Boca Raton, FL. p. 17.\n\n#Schlesinger 1995\n\nSmall changes in carbon pools have drastic effects in the global climate system (Schlesinger, 1995). \n\nLosses in soil organic matter can exacerbate global warming, but increases in soil organic matter can slow the rate of atmospheric CO2 release and \"provide a negative feedback\" to global warming (Schlesinger, 1995). "},{"_id":"68601e50926d19dd38000098","treeId":"641e9e3b83e7b085f200008f","seq":7422081,"position":17.5,"parentId":"641e9e5483e7b085f2000091","content":"#Silver et al., 2010\n\nRangeland ecosystems cover half of the land area of California. \"This large land area, coupled with the propensity of grasses to allocate a considerable proportion of their photosynthate belowground, leads to high soil carbon (C) sequestration potential\"\n\nAnnual grasslands typical of Mediterranean climates \"differ in their life history strategies from the well-studied perennial grasslands of other regions and thus may also differ in their soil C pools and fluxes\"\n\nRangeland soils have been pinpointed as having high sequestration potential due to their large land coverage and ability to \"drive considerable belowground allocation by rangeland plants\". \n\nHigh root biomass contributes to soil C directly through organic matter inputs and indirectly through increased soil aggregation and the formation of recalcitrant humic substances (EX QUO)\n\n\"Regional-scale soil C analyses that include information on patterns in climate, soil type, cover type, or management allow us to explore the relative sensitivity of soil C pools to the environment and to management practices... This information can then be used to identify promising approaches and technologies for C seqeustration\" \n\nCA rangelands differ from perennial temperate grasslands found in the Midwest. Cool wet winters and warm dry summers `lead to` grasslands characterized by annual grasses and forbs which die during dry, warm months and create thick surface litter that protects the soil until the wet season comes. \"This life history strategy\" favors lower root-shoot allocation and shallower rooting depth than perennial grasslands, as no active plant biomass occurs over the dry summer months. \"could lead to lower soil C storage relative to perennial grasslands\"\n\nIn CA annual grassland, each \"season's peak aboveground biomass is equivalent to its ANPP, partially influenced by temperature, precipitation, soils, and the amount of residual dry matter\"\n\nGrazing management in annual grasslands usually considers the relationship between RDM and ensuing year's productivity.\n\n\"Understanding patterns in soil C storage is a first step to exploring soil C sequestration potential\" \n\n\"The wide range in soil C pools in CA's rangelands across similar soil types and climate suggests considerable potential to increase soil C storage in these ecosystems through management\" "},{"_id":"68603569926d19dd38000099","treeId":"641e9e3b83e7b085f200008f","seq":7422122,"position":1,"parentId":"68601e50926d19dd38000098","content":"California annual grasslands differ from their Midwestern counterparts, perennial temperate grasslands. California is characterized by wet winters and dry summer, with grasslands dominated by annual grasses and forbs which die during dry, warm summer months and create thick surface litter (Silver et al., 2010). \n\nCalifornia annual grasslands experience a period of annual grass death during dry, warm summer months, which creates a generally shorter root system than perennial grasslands. This is speculated to lead to lower soil C sequestration rates relative to perennial grasslands (Silver et al., 2010). \n\nGrazing management traditionally utilized in annual grasslands extrapolates a delicate balance between residual dry matter and the following year's productivity (Silver et al., 2010). \n\nSoil carbon analyses performed on a regional scale are an effective way to trace the sensitivity of soil carbo pools to the environment and management practices. These analyses should include information on climatic patterns, soil type, cover type, and management (Silver et al., 2010). \n\nA review of soil analyses in California annual grasslands found a wide range of soil carbon across similar soil types and climate, suggesting \"considerable potential\" to increase soil carbon sequestration through changing management (Silver et al., 2010). "},{"_id":"66be2e3ed93604202a00002e","treeId":"641e9e3b83e7b085f200008f","seq":6785335,"position":18,"parentId":"641e9e5483e7b085f2000091","content":"#Soussana2004 \n\nIn grasslands, three major greenhouse gases are exchanged at the atmosphere-biosphere level. Carbon dioxide is exchanged with soil and vegetation, nitrous oxide is released by soils, and methane is emitted with livestock and can be taken in by soils (Soussana et al., 2004). \n\nIn intensive grazing systems, up to 60% of above-ground biomass is eaten by herbivores each grazing cycle (Soussana et al., 2004).\n\nAnnual net ecosystem production of grasslands can be 1-6tC/ha/yr and is typically limited by water and/or nutrients (Soussana et al., 2004). \n\nSoil carbon stocks in grasslands have higher spatial variability than crop land (Soussana et al., 2004). Conversion of grassland to arable land can cause a 25-43% decline in SOC from 0-120 cm. However, converting cropland to grassland can reverse the decline and increase SOC by 0.5tC/ha/yr. Sousanna et al proposes that the rate of SOC growth in situation is slow and does not regain the level it held before the grassland was first plowed after 50 years. \n\nSoussana et al made four recommendations in their 2004 study. The authors recommended reducing N fertilizer inputs in highly intensive grasslands, increasing duration of grass fallows, convert fallows to grass-legume mixtures or permanent grasslands, and moderately intensifying nutrient-poor permanent grasslands (Soussana et al., 2004). \n\nA French study proposed that restoring half the amount of land lost since the 1970's to permanent grassland for 20 years would be equilivalent to only 10% of France's annual CO2 emissions from fossil fuels (Soussana et al., 2004). \n\nA 2004 French study utilized several modeling systems to demonstrate variabilities in a large database collected in 2002. The INRA `??` collected 19,000 unpublished references and 1000 literature references to pool data taken from the upper 30 cm of soil. The models attempted to quantify the fluxes in SOC stock and GHG changes, and generalized conclusions regarding the kinetics of SOC accumulation. The kinetics of SOC accumulation following changes in management practices appear to be non-linear and assymetric: the change is more rapid in the early years after changing land management, and accumulation is much slower than the previous release under the first management regime (Soussana et al., 2004). \n"},{"_id":"66be6496d93604202a00002f","treeId":"641e9e3b83e7b085f200008f","seq":6785330,"position":19,"parentId":"641e9e5483e7b085f2000091","content":"#Batjes 1998\n\nThe soil carbon fraction is largely associated with organic matter, but in semi-arid and arid soils, calcareous CO3-C `??` can be significant and charcoal is present in areas subject to frequent fires (Batjes 1998).\n\nSoil has 2.5 times more organic C than vegetation and twice the C than the atmostphere (Batjes 1998). \n\nThe topsoil organic matter is involved in nutrient cycling and atmospheric gas exchange (Batjes 1998). \n\nSoil organic matter characteristics are influenced by moisture status, soil temperature, oxygen supply (drainage), soil acidity, soil nutrient supply, clay content, and mineralogy (Batjes 1998).\n\nThe rate of turnover of organic matter can range from 15-40 years in the upper 10 cm and over 100 year for subsoil below 25 cm (Batjes 1998). \n\nIt can take from 10 to 50 years after each disturbance to resolve a new equilibrium of soil carbon (Batjes 1998). The equilibrium established after implementation of new land management can be lower or higher than the original amount. \n\nVariables controlling soil C seq, like climate change and rising atmospheric levels of CO2, are \"highly interactive and complex\" and, simply put, there are no easy answers (Batjes 1998). \n\nPractices that Batjes recommends to enhance soil C seq are to account for different soil types, suitability, and factors for soil formation before cultivating or grazing land. Semi-arid grassland management can focus on reduction of burning, improving the soil nutrient status, and introducing improved grasses and legumes in combination with controlled stocking rates (Batjes 1998). \n\n\"The role of agriculture in sequestering of organic C by soils remains ambiguous. The overall picture is complicated by technological, social, economical and cultural factors\" (Batjes 1998). \n\nThere is a historical correlation between decreases in soil carbon content and low production levels, inadequate fertilizer application, removal of crop residues, and intensive tillage practices (Batjes 1998). \n\n\n"},{"_id":"66bf9a3fd93604202a000032","treeId":"641e9e3b83e7b085f200008f","seq":6785333,"position":19.25,"parentId":"641e9e5483e7b085f2000091","content":""},{"_id":"66bf9a0fd93604202a000031","treeId":"641e9e3b83e7b085f200008f","seq":6785332,"position":19.5,"parentId":"641e9e5483e7b085f2000091","content":""},{"_id":"66bf9a0ed93604202a000030","treeId":"641e9e3b83e7b085f200008f","seq":6785343,"position":20,"parentId":"641e9e5483e7b085f2000091","content":"#Soussana2010\n\nGrasslands cover a quarter of the earth's land surface (Soussana et al., 2010). \n\nRangelands are found on every continent and contribute to livelihoods of 800 million people. Livestock uses 3.4 billion hectares of grazing land, in addition to feed produced on a quarter of the world's crop land (Soussana et al., 2010).\n\nAgricultural soils have lost an estimated 50 Gt of carbon (Soussana et al., 2010). \n\nGrassland soils are a major focus of carbon sequestration research, because they are typically rich in SOC. Grassland soils have active rhizodeposition and earthworm activity that promote aggregate formation that microbiota form into micro-aggregates, the form in which SOC stabilizes for extended periods (Soussana et al., 2010). \n\nSOC can stay in soils for hundreds of years if left undisturbed (Soussana et al., 2010). \n\nNative prairie soil sites in the US Great Plains were subjected to 14C-dating that found mean residence time of SOC in soil increased but the concentration decreased with depth- however, \"substantial amounts of SOC\" were dated back several millenia (Soussana et al., 2010). \n\nSOC needs protection from microbial decomposition in order to stabilized long-term. SOC in deeper soils is distanced from the energy supply from decomposing surface organic matter. When tilling mixes soil layers and breaks up soil aggregates, it also accelerates SOC decomposition and prevents stable SOC sequestration (Soussana et al., 2010). \n\nSoil disturbance, vegetation degradation, fire, erosion, nutrient shortage, and water deficit all lead to rapid loss of SOC (Soussana et al., 2010). \n\nThere are two practical ways to measure or estimate SOC seq: directly by measuring changes in C pools or indirectly by measuring C fluxes. Spatial variability is the main concern that limits accuracy of direct measurements- to decrease variability, samples should be taken to different depths and avoid pastures with concentrated feces on the surface (Soussana et al., 2010). \n\nSOC accumulates over time in a non-linear fashion. Soussana et al estimates that converting cropland back to grassland for 20 years restores 18% of native C stocks in moist climates and 7% in temperate dry climates (Soussana et al., 2010). \n\nMany SOC studies focus on the 0-30cm soil strata, as most accumulation occurs in those layers, but lose can occur from deeper horizons (Soussana et al., 2010). \n\nSoussana et al conducted a meta-analysis of 115 studies in pastures and grazing land. They found that improved management increased SOC levels in 74% of the studies. Improved management practices included fertilization, grazing management, conversion from cultivation, and improved grass species (Soussana et al., 2010). \n\nAn analysis of 115 studies in pastures found that light grazing increased SOC more than exclosure and heavy grazing (Soussana et al., 2010). However, the article did not specify whether the heavily grazed pastures were on a continuous or rotational grazing system.\n\nNitrous oxide and methane emissions are often expressed in terms of CO2 equivalents, in an attempt to keep standard parameter (Soussana et al., 2010). \n\nSoil C stocks in grassland ecosystems are vulnerable to climate change (Soussana et al., 2010). \n\n \n\n\n"},{"_id":"66c01b1bd93604202a000034","treeId":"641e9e3b83e7b085f200008f","seq":6785383,"position":22,"parentId":"641e9e5483e7b085f2000091","content":"#Pringle et al., 2011\n\nLittle is known about how cattle grazing affects SOC (Pringle et al., 2011). \n\nPringle et al utilized linear mixed models to propose how grazing pressure and soil type affects SOC and stable carbon isotope ratio of SOC and explored the amount of soil sampling required to adequately determine baseline SOC. They found that soil type and grazing pressure interact to influence SOC to 30 cm depth. At 50 cm, there was no grazing effect but the soil type remained a significant factor. They recommended to cattle-grazing properties in tropical rangelands of Australia to divide properties into units of uniform soil type and grazing management, and use stratified simple random sampling to take 25 soil sampling locations about each unit, with at least 2 samples collected per soil stratum. They proposed that 25 soil samples per unit is adequate to estimate baseline mean SOC to within 20% of true mean to depth of 30 cm (Pringle et al., 2011). \n\nThe substantial area of the globe devoted to grazing means that minor changes in SOC can cause proportionately large changes in C seq worldwide (Pringle et al, 2011).\n\nSpatial variation is further compounded by inherent soil variation, microclimate, fire history, tropography, and complex plant communities, which makes even the smallest scale of management tricky to sample precisely (Pringle et al., 2011). \n\nStable carbon isotope ratio data may help to gain a more complete understanding of SOC dynamics and sequestration (Pringle et al., 2011). \n\n"},{"_id":"66c02d0bd93604202a000035","treeId":"641e9e3b83e7b085f200008f","seq":6792443,"position":23,"parentId":"641e9e5483e7b085f2000091","content":"#Pineiro et al., 2010\n\n\"Soil organic matter is the main reservoir of SOC and soil organic nitrogen in rangelands and determines soil fertility, water retention, and soil structure\" (Pineiro et al., 2010)\n\nIn arid rangelands, SOC accumulation is limited by water availability and C uptake- also known as net primary productivity (Pineiro et al., 2010). \n\nConceptual models estimate that changes in SOC stocks are determined by the balance between C and N inputs and outputs, more directly by NPP, respiration, and carbon outputs (plant production). Storage of SOC is determined by the proportion of NPP that is allocated to belowground organs. Climate, biota, time, topography, and parent materials are other factors that control SOC accumulation. Pineiro et al suggests that these contextual factors operate via cascade effects through shorter-term controls (Pineiro et al., 2010).\n\nA 2010 global literature review found that SOC changed under contrasted grazing conditions across climactic gradients, and that the factors that control SOC in a grazed ecosystem are more complex than we currently think they are. General patterns that the study noted were that root contents, the primary control of SOC formation, were higher in grazer than ungrazed systems at the most arid and most tropical sites but were lower at temperate sites. The increased root biomass should increase SOC because of greater C inputs to the soils (Pineiro et al., 2010). \n\nGrazing can change how carbon allocates in the soil. Belowground biomass enters the soil directly and contributes more to soil organic matter formation than aboveground productivity. Grazing changes the proportion of NPP allocated to aboveground or belowground organs (Pineiro et al., 2010). \n\nOne researcher argues that grazing can affect NPP indirectly by altering species composition or soil resources by decreasing water availability (Pineiro et al., 2010). \n\nMore efficient Nitrogen conservation can affect SOC stocks, according to Pineiro et al. The authors recommended avoiding \"unwanted\" N emissions from excessively loading grazing systems with nitrogen inputs, and that N dynamics would allow increased C seq in soils, and increased soil fertility (Pineiro et al., 2010). "},{"_id":"66bfef9ad93604202a000033","treeId":"641e9e3b83e7b085f200008f","seq":6895179,"position":23.5,"parentId":"641e9e5483e7b085f2000091","content":"#Whalen et al., 2003\n\n\"Grazing lands contain 10-30% of the world's SOC and have potential to act as a significant sink of atmospheric CO2\" (Whalen et al., 2003). \n\nThe Great Plains have lost 24-60% of their SOC pool from 100 years of cultivation, which breaks up soil aggregates and fragments organic matter, increasing the rate of decomposition and stimulating emission of CO2 from soils (Whalen et al., 2003). \n\nCrop systems have decreased C input since most above-ground biomass is removed and annual crops produce less root biomass than perennial plants (Whalen et al., 2003).\n\nConverting cropland to grasslands in semi-arid Great Plains don't always work out as planned, although they can usually be restored by seeding non-native perennial grasses (Whalen et al., 2003). Understandably, total C, N, and microbial biomass are lower in recently established grasslands and can take over 50 years to approach native levels (Whalen et al., 2003). \n\nA crucial foundation in any system aiming to increasing SOC retention is to establish ground cover. Permanent soil cover quickly stabilizes water retention and reduces quantities of sediments, nutrients, and agricultural chemicals transported to surface waters within a few years (Whalen et al., 2003). \n\nEXPERIMENT: A study in the Great Plains chose 3 sites that represented 3 climactic gradients and cultivated native rangelands. In each site, plots were abandoned, seeded with non-native perennial grasses to establish permanent cover, or converted to annual crop production. Samples were obtained from 0-15 cm in depth. The soil bulk density was lower in the undisturbed native rangeland than modified plant communities, and the total C, N, and P contents declined with cultivation. The authors called for a need to collect deeper samples to determine if net gains or losses had occurred throughout the soil profile or were concentrated in the topsoil. The authors found that establishment of perennial grasses or legumes on formerly cultivated land could slow or reverse depletion of SOC, and stabilization or loss of C and N from modified plant communities is affected by climate as well as quantity and chemical characteristics of residues produced by plants (Whalen et al., 2003). "},{"_id":"66c941bc48d5a85245000036","treeId":"641e9e3b83e7b085f200008f","seq":6895202,"position":24,"parentId":"641e9e5483e7b085f2000091","content":"#Lal2004 (Lal, 2004)\n\nDr. Rattan Lal recommends these strategies to increase SOC: soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands (Lal, 2004). \n\nThe range at which C seq can offset fossil fuel emissions varies from studies depending on which modeling aspects they are focusing in on, but Dr. Rattan Lal puts the number at 0.4-1.2 Gt of carbon per year, or 5-15% of global fossil-fuel emissions (Lal, 2004). \n\n2500 Gt of carbon are contained in our world's soil organic carbon pool, of which 1550 Gt is organic and 950 Gt is inorganic. In comparison, it is 3.3 times atmospheric carbon levels and 4.5 times the size of the biotic pool (Lal, 2004). \n\nMost global soils range from 50-150 tons per hectare of carbon in the 100 cm depth (Lal, 2004). \n\nConverting natural landscapes to crop production can deplete SOC by 60% in temperate regions and 75% or more in tropical climates (Lal, 2004).\n\nSOC loss is exaggerated in agricultural ecosystems with severe soil degradation. Carbon loss from soils is emitted directly into the atmosphere and reduces soil quality and biomass productivity, and negatively impacts water quality (Lal, 2004). \n\nThe definition of C sequestration is the act of transferring atmospheric CO2 into long-lived pools and storing it securely in such a way that it's not immediately reemitted (Lal, 2004). Carbon sequestration can also refer to the act of increasing the SOC pool through management practices (Lal, 2004). \n\nThe rate of increasing SOC pools is nonlinear. Lal suggests it follows a sigmoid curve, hits the maximum rate 5-20 years after management changes and then continues until the SOC falls into equilibrium. Rates are inherently dependent on soil characteristics and climate as well as management. Dry and warm regions are subject to slower rates, upwards rates of 150 kG/ha/yr, while humid and cool climates could see C seq rates upward of 1000 kg/C/ha/year (Lal, 2004). These rates could potentially be sustained until the soil sink capacity is filled. \n\nManagement practices that are recommended by Lal add biomass to the soil, cause minimal soil disturbance, improve soil structure, enhance soil microbiota biodiversity, and strengthen mechanisms of nutrient and water cycling (Lal, 2004). \n\nWhile C can be sequestered as secondary carbonates, that rate is low and not the subject of focus as much as SOC is (Lal, 2004). \n\nWhile soil carbon sequestration may not be the end-all of climate change solutions, it shows potential to mitigate the effects of climate change until fossil fuel alternatives take effect (Lal, 2004). \n\nCarbon is only one elemental constituents of humus. Sequestering 1 Gt of C in soil requires 80 Mt N, 20 Mt P, and 15 Mt K (Lal, 2004). Nutrient cycling needs to be effective for the nutrients necessary for C sequestration to be available.\n\nSoil erosion is a key factor in degraded land, and also removes SOC by wind and water-borne sediments transported away from the soil during erosion processes (Lal, 2004). \n\nCarbon markets have been in use since 2002, mostly in European Union countries. The \"commodification of soil C is important for trading C credits\" (Lal, 2004). \n\nCarbon sequestration is a bridge between 3 global issues: climate change, desertification, and biodiversity (Lal, 2004). Regardless of the climate change debate, it is a crucial issue that could increase productivity and water quality and restore degraded ecosystems (Lal, 2004). \n\nAgriculturally developing nations, especially those in tropical climates where dynamic soil processes exacerbate rates of SOC accumulation or loss, have the greatest need for change. Currently, the C sink capacity is high, but the rate of C seq is low and complicated by limited infrastructure and resource-poor agricultural systems (Lal, 2004). \n\nGenerally, soil C seq by adapting recommended management practices is a natural, cost-effective, and environmentally-friendly process (Lal, 2004). \n\n\"Soil sink capacity and performance are related to clay content and mineralogy, structural stability, landscape position, moisture and temperature regimes, and ability to form and retain stable microaggregates\" (Lal, 2004). \n\n"},{"_id":"66c9726f48d5a85245000037","treeId":"641e9e3b83e7b085f200008f","seq":6792674,"position":25,"parentId":"641e9e5483e7b085f2000091","content":"#Jones2008\n\nIf 2% of Australia's agricultural land increased their SOC stocks by 0.5% in the top 30 cm, it would sequester the nation's annual emissions of CO2 (Jones, 2008). \n\nIn essence, C seq is act of storing atmospheric carbon in the soil as humified organic carbon (Jones, 2008). \n\nSOC can only storage permanently in wood or humus. To turn air into soil, photosynthesis converts CO2 to sugars, those simple sugars are exudated from plant roots and humification occurs in biologically active soil aggregates (Jones, 2008). \n\nIn its most simple form, humification is joining simple carbon compounds together into more complex and stable molecules. It requires soil microbiota including mycorrhizal fungi, nitrogen fixing bacteria, and phosphorus solubilizing bacteria (Jones, 2008). \n\nMost conventional SOC models assume that the only C input in soils comes from biomass inputs from decomposition of surface litter and belowground roots. However, when carbon enters soil as plant material, it decomposes and is returned to the atmosphere as carbon dioxide (Jones, 2008). \n\n\"Soluble carbon\" is the idea of simple sugars from the plant being channeled into soil aggregates via the hyphae of mycorrhizal fungi, and can be rapidly stabilized by humification (Johnes, 2008). \n\nMycorrhizal fungi is recognized in the agricultural world as decomposing fungi that obtains energy from decomposing organic matter and important for soil fertility and structure (Jones, 2008). Conventionally managed agricultural systems only see mycorrhizal fungi with small hyphal networks, because soil-disturbing acts like plowing and fungicide destroys the hyphae networks.\n\nMycorrhizal fungi transports nutrients, including P, K, and Zn, in exchange for carbon from their plant hosts. They connect individual plants below ground and can facilitate transfer of nutrients between species (Jones, 2008).\n\nHumification forms a stable and inseparable part of the soil matrix that can remain intact for hundreds of years (Jones, 2008). \n\nHumus differs from the labile pool of soil organic carbon that forms in the topsoil. Labile carbon is formed from biomass inputs, and humified carbon is secreted from exudation from plant roots to mycorrhizal fungi and microflora, and can form deep in the soil profile (Jones, 2008). \n\nConsidering the so-called \"liquid carbon pathway\", C seq rates can range from 5-20 tCO2/ha/year (Jones, 2008). \n\n"},{"_id":"66c98ca848d5a85245000038","treeId":"641e9e3b83e7b085f200008f","seq":6792688,"position":26,"parentId":"641e9e5483e7b085f2000091","content":"#Jones2006\n\nLoss of ground cover, intensive cultivation, bare fallows, stubble and pasture burning, and continuous grazing are all factors that cause loss of SOC (Jones 2006).\n\n\"Grazing animals, plants, soil biota and soils have co-evolved for over 20 million years, resulting in highly complex and sensitive inter-relationships\" (Jones, 2006). \n\nA proposed method for how grazing soil carbon is how the plant readjusts for biomass loss after grazing. More carbon is contained in the roots than the leaves of the plant, and when the leaves are removed by grazing, and plant responds by readjusting its biomass balance. Some carbon is mobilized to the crown for production of new leaves, some is lost to the soil as root decomposition, and some is actively exuded into the rhizosphere. Thus, each grazing event becomes a \"carbon injection\" opportunity (Jones, 2008). \n\nPlants that are grazed continuously have poorly developed root systems and little C available for exudation into the soil (Jones, 2006).\n\n "},{"_id":"66c9b7c648d5a8524500003b","treeId":"641e9e3b83e7b085f200008f","seq":6792759,"position":29,"parentId":"641e9e5483e7b085f2000091","content":"#Waltman et al., 2010\n\nIn the next century, the world faces a 2 degrees C or greater air temperature increased if GHG are not curtailed (Waltman et al., 2010).\n\nFortunately, the agricultural sector has significant opportunities to mitigate GHG emissions, and currently one substantiated option is to increase carbon sequestration (Waltman et al., 2010). \n\n"},{"_id":"66c9bcfa48d5a8524500003c","treeId":"641e9e3b83e7b085f200008f","seq":6792785,"position":30,"parentId":"641e9e5483e7b085f2000091","content":"#Ellert et al., 2002\n\nLarge quantities of carbon are already present in soils, so sensitive methods are needed to detect small changes in soil C storage (Ellert et al., 2002). \n\nQuantitative assessments of SOC are crucial to describe ecosystem function (Ellert et al., 2002). \n\nSOC influences nutrient and pollutant availability, soil structure, and erosion properties (Ellert et al., 2002). \n\nOne of the first mentions of carbon sequestration were a 1977 study that proposed C emissions could be offset by planting massive quantities of trees (Ellert et al., 2002). \n\nA 2002 study compared treatments in a randomized design that were treated with a known quantity of coal to compare the accuracy of soil sampling carbon measurements. The total C and N was analyzed using a CN analyzer, like our experiment. The \"microsite approach\" as the researchers called it, \"successfully resolved small changes\" in soil C storage relative to the much larger quantities already present. They did use bulk density corrections to correct for the differences in soil mass. \n\n"},{"_id":"66c9caaf48d5a8524500003d","treeId":"641e9e3b83e7b085f200008f","seq":6792809,"position":31,"parentId":"641e9e5483e7b085f2000091","content":"#Conant et al., 2002\n\nSoil carbon is tricky to detect and quantify, largely to due inherent spatial variability that limits precision the ability to detect change (Conant et al., 2002). \n\nConant et al compared samples from 4 sites of unique climatic and management combinations, and found that small changes in SOC are detectable, but only with careful and controlled measurement (Conant et al., 2002). \n\nThey found greater spatial variabilities in forested areas than cultivated sites (Conant et al., 2002). \n\nA 2002 study found that six cores per microplot is \"adequate\" to represent a range of soil samples within more uniform sites: however, this method is not appropriate for all systems (Conant et al., 2002). They recommended that multiple microplots be sampled in the future to decrease variability.\n\nConant et al reommended to resample the same microplots for future measurements, as this enhances statistical power and allows changes to be detected years earlier (Conant et al., 2002). \n\nThe minimum detectable difference is inversely related to the number of samples required (Conant et al., 2002)> \n\n"},{"_id":"66c9d79a48d5a8524500003f","treeId":"641e9e3b83e7b085f200008f","seq":6794074,"position":33,"parentId":"641e9e5483e7b085f2000091","content":"#DeDeyn et al., 2008\n\nSoil carbon storage is a key component of the global carbon cycle (De Deyn et al., 2008). \n\nRapid changes can quickly make soil carbon sinks into sources for atmospheric carbon (De Deyn et al., 2008). \n\nNPP is determined by equilibrium between carbon input through photosynthesis, and carbon loss through plant respiration and soil respiration (De Deyn et al., 2008). \n\nNon-respiratory losses of carbon include decomposition processes, charring or burning, and volatilization and leaching or organic compounds (De Deyn et al., 2008). \n\nIt is thought that the maximum sequestration potential of soils is determined by intrinsic abiotic soil factors like topography, mineralogy, and texture, and that biota-driven factors are a minor factor in soil carbon dynamics (De Deyn et al., 2008). \n\nGeneral plant traits regulate SOC by altering carbon input through NPP and belowground carbon allocation (De Deyn et al., 2008). \n\nFast-growing plant species contribute carbon through root exudate to the soil, while slow-growing species contribute through input of low quality plant material. In biomes with a short growing season and low nutrient availability, SOC input is mainly derived from litter decomposition, but in productive biomes NPP is the main driver of carbon sequestration (De Deyn et al., 2008). \n\nMycorrhizal fungi and nitrogen fixing bacteria are common plant symbionts that can increase plant productivity by attaining and transfering resources (De Deyn et al., 2008). \n\nMF enhances plant nutrient acquisition from soil, reduces soil C loss by immobilizing carbon in the myeclium, extending root lifespan, and importing C to soil aggregates, and are conveniently associated with most terrestrial plant species (De Deyn et al., 2008). \n\n\"Long term enhancement of SOC seq requires sustained primary productivity and efficient feedback between communities of plants and soil biota for carbon and nutrient cycling\" (De Deyn et al., 2008). \n\nMaximizing the balance between soil carbon input and output is the best way to enhance SOC seq (De Deyn et al., 2008). \n\nDe Deyn et al states that we don't yet know enough about the link s between aboveground and belowground plant traits to be able to make accurate predictions about impact on SOC seq or response to global change (De Deyn et al., 2008). \n\nThe scientific community needs to be open to new plant traits and pathways of carbon flow, as we discover more about soil microbiota and their ecosystems (De Deyn et al., 2008). "},{"_id":"66cb0ed848d5a85245000040","treeId":"641e9e3b83e7b085f200008f","seq":6794098,"position":34,"parentId":"641e9e5483e7b085f2000091","content":"#Jastrow et al., 2007\n\nJastrow et al recommend reducing C turnover and increasing residence time in soils to maximize soil C seq (Jastrow et al., 2007). \n\nBiochemical alteration is the process of transforming SOC to chemical forms that are more resistant to decomposition and are incorporated into soil solids (Jastrow et al., 2007). \n\nPhysicochemical protection is the ability of organomineral interactions to protect SOC from biochemical attack (decomposition) (Jastrow et al., 2007). \n\nThere are several ways to stabilize SOC to protect it from decomposition. These include occluding SOC within aggregates, depositing it in pores inaccessible to decomposers, and sorption `??` to mineral and organic soil surfaces (Jastrow et al., 2007).\n\nChanging management practices to those that shift the soil biochemical environment to favor fungi can reduce the rates of SOC decomposition and enhance sequestration. Practices that show potential for accomplishing this include planting perennial species, reducing tillage, maintaining neutral soil pH, ensuring adequate drainage, and minimizing erosion (Jastrow et al., 2007). "},{"_id":"66cb246f48d5a85245000042","treeId":"641e9e3b83e7b085f200008f","seq":6794142,"position":36,"parentId":"641e9e5483e7b085f2000091","content":"#Donovan2013 (Donovan, 2013)\n\n\"Soil carbon measurement is as much a social issue, involving beliefs and attitudes, as it is a technical one\" (Donovan, 2013)\n\nThe global issue of carbon has many contexts and perceptions, as well as different uses to people and producers (Donovan, 2013). This complicates the seemingly simple idea of measuring soil carbon change. \n\n\"Carbon is life and food, and moves from atmosphere to plants and soils and back in a grand cycle that is sometimes called the circle of life\" (Donovan, 2013). \n\nPeter Donovan, creator of the Soil Carbon Coalition, writes that \"soil carbon may be one of the easiest and most practical ways to monitor the work of the biosphere on land\" (Donovan, 2013). \n\nThe major sources of uncertainty in SOC sampling is sampling error and non-random selection of sampling sites (Donovan 2013).\n\nTo maximize the chance of detecting and measuring change, Donovan recommends waiting longer between samplings (Donovan, 2013). This would also aid to distinguish between year-to-year weather variability (Donovan, 2013). \n\nThere are 3 forms of carbon in soil. The largest fraction is organic soil carbon, which is derived from living tissue. It is critical in the formation of soil aggregates but is typically the least stable form of carbon. Charcoal is derived from living tissue as well, so is considered organic and is also more resistant to decomposition. Inorganic soil carbon is the most stable form because it is protected from decomposition but typically changes at a slower rate (Donovan, 2013). \n\nDonovan lists 5 laboratory techniques to measure soil carbon directly from soil samples. These include elemental analysis by dry combustion, acid treatments, loss on ignition, carbon fractions, and soil respiration. Of these, elemental analysis by dry combustion is considered the most accurate that is likely to detect change in the organic carbon fraction but measures total soil carbon (inorganic and organic) (Donovan, 2013). \n\nSampling from different horizontal strata reduces variability since deeper layers have less spatiotemporal variation and can help to account for differences in soil types, vegetation cover, management, etc. (Donovan, 2013). \n\nMASS OF CARBON: TOTAL CARBON = FRACTION CARBON (DECIMAL) X DENSITY X VOLUME IN CUBIC METERS\n\nSTANDARD ERROR= STANDARD DEVIATION OF ALL SAMPLES DIVIDED BY SQUARE ROOT OF NUMBER OF SOIL CORES\n\nTesting microsites to make broad conclusions about a pasture's soil carbon content is analogous to comparing three tax returns in a small town to gain an accurate view of the average personal income (Donovan, 2013). "},{"_id":"66f356796c36c33b08000046","treeId":"641e9e3b83e7b085f200008f","seq":6824058,"position":40,"parentId":"641e9e5483e7b085f2000091","content":"#Lal2007\n(Lal et al., 2007)\n\nThe definition of carbon sequestration, according to the Department of Energy, is \"the provision of long-term storage of carbon in the terrestrial biosphere, underground, or the oceans so that the build-up of CO2 will reduce or slow\". Sequestration is either natural or anthropogenic-driven. Natural sequestration is limited to terrestrial sequestration in soil and trees, while anthropogenic-driven geologic sequestration include such man-made technologies as injection of liquified CO2 into rock formations, old oil wells, etc. (Lal et al., 2007).\n\nSoil quality is defined as the combination of characteristics that enable soils to perform a wide range of functions (Lal et al., 2007).\n\nManagement choices affect the amount of soil organic matter, soil structure, soil depth, and water and nutrient-holding capacity (Lal et al., 2007).\n\nPastures and rangelands cover 55% of United States's total land surface, and represent the largest and most diverse resource in the world (Lal et al., 2007). \n\nThe SOC seq potential for US cropland and grazing land is 180Mt SOC/yr (Lal et al., 2007)."},{"_id":"66f367166c36c33b08000048","treeId":"641e9e3b83e7b085f200008f","seq":6824568,"position":42,"parentId":"641e9e5483e7b085f2000091","content":"#Fynn et al., 2010\n\nThe term \"rangelands\" includes grasses, savannas, steppes, shrub lands, desert, and tundra (Fynn et al., 2010).\n\nA small change in SOC could have a large impact on overall GHG, since US rangelands represent such a large surface area (Fynn et al., 2010). \n\nUS grazing lands could potentially sequester up to 198 million t CO2 /yr from atmosphere for 30 years (Fynn et al., 2010). \n\nEach ton of C stored in soils removes 3.67 t of CO2 from the atmosphere (Fynn et al., 2010). \n\nSOC is 50% of soil organic matter (Fynn et al., 2010).\n\nManagement recommendations made by Flynn et al for increased carbon sequestration include adjustments in stocking rates, introduction of grasses on degraded lands, managing invasive species, reseeding grassland species, riparian zone restoration, and introduction of biochar to soils (Fynn et al., 2010).\n\nThe basic idea of a \"carbon market\" is to instill a financial incentive to producers to sequester soil organic carbon on their land. Increased soil carbon levels would be converted to verified emissions reductions to use within an offset market, cap and trade system, or other credit program (Fynn et al., 2010).\n\nIn terms of sampling, accuracy costs more and cheaper methods are traditionally less accurate (Fynn et al., 2010). \n\n\"Rather than tie a protocol to the limitations of one particular method, it is logical to combine the strengths of different methods into a single methodology, which may be updated as economics and technical advances allow\" (fynn et al., 2010).\n\nCarbon enters the plant from the atmosphere, and becomes soil carbon through processes of above and below-ground decomposition, root decomposition, and the release of exudates from plant roots in the soil (Fynn et al., 2010).\n\n90% of carbon in rangeland systems is in the soil (Fynn et al., 2010).\n\nSOC accumulation is directly correlated to precipitation and inversely correlated to temperature (Fynn et al., 2010).\n\nThere are 3 major ways to protect soil organic carbon from microbial decomposition. Chemical stabilization is the bonding of positively charged SOC molecules to negatively charged iron and clay anions. Physical protection is holding soil aggregates together with \"glues\" like glomalin, and biochemical recalcitrance is characteristics of carbon substrates that are consumed by microbes but remain un-decayed compounds (Fynn et al., 2010).\n\nTwo types of carbon in each accumulated pool have different mean residence times. The light fraction, made of fresh plant materials subject to rapid decomposition, turnover within a few years at most. Early changes in SOC from management changes occur in this fraction, which is also known for its high spatiotemporal variability. The heavily occluded fraction, composed of carbohydrates and humic materials stabilized in clay complexes, can remain in soil for hundreds to over a thousand years (Fynn et al., 2010).\n\nTypically, soils accumulated carbon during plant growth and lose carbon during dormancy (Fynn et al., 2010).\n\n13.6 million acres make up California annual grasslands, which subdivide into inland valley grassland, coastal prairie, and coast range grassland. The plant communities are now dominated by exotic annual grasses brought from Mediterranean regions by Spanish explorers (Fynn et al., 2010).\n\nA rangeland soil carbon sampling methodology should use several methods in combination, which can be placed along a spectrum with practicality at the cheapest end and high confidence levels at the expensive end (Fynn et al., 2010). \n\nThe challenge in determining how management practices affect soil carbon sequestration lies in determining the relationships among precipitation, stocking rate, and carbon dynamics (Fynn et al., 2010).\n\nVariability in sampling can be minimized by lengthening the time between samplings, or increasing the space between samples to cover more of the landscape (Fynn et al., 2010)>\n\nDirect methods of SOC measure directly from a soil sample, while indirect methods rely on modeling to predict the relationship between variable and carbon content (Fynn et al., 2010),\n\nThree uses of indirect measurement methods may assist in verifying direct measurement findings. They include the use of process-based or mechanistic models, remote sensing via satellite, and land use history and databases (Fynn et al., 2010). \n\n"},{"_id":"66f391646c36c33b08000049","treeId":"641e9e3b83e7b085f200008f","seq":6824569,"position":43,"parentId":"641e9e5483e7b085f2000091","content":"#Friedman et al., 2001\n\nImproving soil quality is crucial to achievement of water quality, air quality, and carbon sequestration goals (Friedman et al., 2001).\n\nUsually, testing for soil quality includes a minimum data set that utilizes indicators of microbial biomass C and N (Friedman et al., 2001)."},{"_id":"66c9d53b48d5a8524500003e","treeId":"641e9e3b83e7b085f200008f","seq":6895252,"position":47,"parentId":"641e9e5483e7b085f2000091","content":"#NRCS1996\n\n\"Rangelands trap and store carbon and thus reduce atmospheric greenhouse gases, store water, and filter impurities from water\" (NRCS, 1996).\n\nAmerica's rangelands deteriorated rapidly and significantly during the late 1800s (NRCS, 1996). "}],"tree":{"_id":"641e9e3b83e7b085f200008f","name":"Senior Thesis","publicUrl":"senior-thesis"}}