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Maintaining living roots in the soil provides a source of carbon that fuels microbial processes and sustains the intricate soil food web necessary for a healthy agroecosystem. As introduced in the Role of Carbon in Agriculture section, plants naturally remove carbon dioxide from the atmosphere and transform the gas into organic compounds - carbohydrates- through photosynthesis. Plants then store the organic compounds as a component of their biomass, use them as an energy source through respiration, or exude the compounds directly into the soil through their roots through the liquid carbon pathway shown to the right (18). Similar to how humans shed small skin particulates, plants also shed root cells as they grow and senesce or age. Because carbohydrates consist of molecules of sugar bound together, the sticky, viscous compounds help soil particles aggregate in clumps, allowing larger soil pores to form. These pores are necessary for soil to retain water, provide space for root establishment and growth, and provide habitat for soil microbes essential for nutrient cycling and other biological processes.
1-Loss of the root cells 2- loss of mucilage (insoluble, sticky substance consisting of protein and sugar substances from plant biomass 3- plant biomass; Jones et al, 2009 (18)
Carbon impacts of maintaining living roots and soil cover
Carbon impacts of maintaining living roots and soil cover
Carbon will continue to increase in the soil as soil organic matter when the inputs (fixed through photosynthesis or as soil amendment) are greater than the outputs (soil respiration).
By maintaining soil cover and living roots in the soil year round, and increasing plant species diversity, soil organic carbon stocks can increase, improving soil health properties. Check out the series of images below. How does increasing the soil cover and continuous living roots impact the levels of carbon dioxide drawn down by the plants? How do the levels of soil carbon change with loss of soil cover?
High Soil Cover: Increasing the capacity to capture carbon dioxide from the atmosphere by increasing plant cover.
Reducing Tillage: Decreasing the rate at which carbon is returned to the atmosphere by decreasing soil respiration losses.
Even when the system is left fallow, or with no crops to contribute to the soil carbon stocks, soil respiration will continue, depleting the soil carbon pool.
High soil coverGraphics created by Ellie Ellis at Colorado State University.
Low soil cover
No soil cover
Assessing Soil Carbon Changes through Cover Crop Additions
Assessing Soil Carbon Changes through Cover Crop Additions
In the scenario to the right from the Allee Demonstration Farm in Iowa, the 60-acre corn-soybean rotation is converted from an intensive/reduced tillage system to no-till with winter cover crop. With this combination of conservation practices, COMET-Farm estimates 61.4 metric tonnes of CO2 equivalent emissions avoided or sequestered, which the amount of carbon dioxide sequestered by 80.2 acres of forest in a year (Check out the EPA GHG Equivalencies Calculator under the Resources tab).
Aggregate Stability and Maintaining Living Roots and Cover
Through maintaining living roots and soil cover throughout the year, carbon is added to the soil improving aggregate stability.
Nutrient Co-benefits of maintaining living roots and soil cover
While maintaining living roots in the soil year round improves soil health through increased carbon additions, leguminous cover crops also provide nitrogen benefits to the soil through their ability to host root associated bacteria that fix atmospheric nitrogen in a form usable for crops. The first image in the carousel below illustrates how nitrogen cycles through an agroecosystem and the second image demonstrates a reduction in the loss of nitrate with the implementation of a rye cover crop. With an increase in nitrogen fixation by leguminous standing crops or simply maintaining soil cover, the need for additional synthetic nitrogen amendments decreases and water quality increases.
Additional Soil Health Co-Benefits of Maintaining Living Roots and Soil Cover
Additional Soil Health Co-Benefits of Maintaining Living Roots and Soil Cover
Benefits of maintaining living roots and soil cover through incorporating cover crops into an annual crop rotation go beyond increasing sequestered soil organic carbon and include: improving aggregate stability and water holding capacity, providing habitat for beneficial soil microbes and macro-invertebrates, opportunity to integrate livestock into cropping systems, reduce erosion, and displacing fertilizer costs and emissions.
Cover Crops & Moisture
Cover Crops & Moisture
Cover Crops & Habitat
Cover Crops & Habitat
Soil cover and maintaining living roots is not exclusive to cover cropping and implementing conservation crop rotations.
Reducing tillage intensity (CPS 329/345) improves crop residue that remains on the soil surface
Mulching (CPS 484) provides erosion control and conserving soil moisture through soil cover
Woody plantings or agroforestry practices provide continuous soil cover and maintain living roots in areas of the working land while protecting productive land and livestock from wind
Herbaceous covers, such as Conservation Cover (CPS 327), Field Borders (CPS 386), Range Planting (CPS 550), and others, also provide soil cover while maintaining continuous living roots.
Check out NRCS's full list of Conservation Practice Standards and/or COMET-Planner's one page summaries of those practices (COMET-Planner only includes 34 practice standards with various implements) under the Resources tab.
Important note:
Important note:
Appropriate cover crops and crop rotations vary depending on climate, cropping system and soil type in a given region
Under a given management scenario, organic carbon stocks will reach an equilibrium point where the soil accumulates no additional carbon, unless additional conservation practices are deployed.
Management activities, such as irrigation and tillage can be detrimental to the influence of crop rotations and cover crops on greenhouse gas capture and emissions.
Continue to explore additional benefits of maintaining living roots and soil cover through the following links under the Resources tab: Cover Cropping to Improve Climate Resilience, USDA Cover Crops and Soil Health, USDA- Cover Crops to provide weed control and forage, and USDA- Benefit and Risk Comparison of Cover Crops
❓Check your knowledge!
Cover cropping and conservation crop rotation are the only ways of maintaining living roots and soil cover. [True/False]
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Discussion board: If you have any questions throughout Module 1, please use the discussion board below to post.
(1) Jones DL, Nguyen C, Finlay RD (2009) Carbonflow in the rhizosphere: carbon trading at the soil–root interface. Plant Soil 321:5–33 From <https://www.researchgate.net/publication/343813762_Rhizosphere_Plant-Microbe_Interactions_Under_Abiotic_Stress>
Kong, A.Y., J. Six, D.C. Bryant, R.F. Denison, et al. 2005. The relationship between carbon input, aggregation, and soil organic carbon stabilization in sustainable cropping systems. Soil Science Society of America Journal, 69:1078‐1085.
Kong, A.Y., J. Six, D.C. Bryant, R.F. Denison, et al. 2005. The relationship between carbon input, aggregation, and soil organic carbon stabilization in sustainable cropping systems. Soil Science Society of America Journal, 69:1078‐1085.
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