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1 1 (December 03, 2020)

handle is hein.crs/govdcsp0001 and id is 1 raw text is: December 3, 2020 Agricultural Soils and Climate Change Mitigation Policymakers, scientists, farmers, and others takeholders have debated the potential of agricultural soils to sequester (store) carbon and help mitigate future climate change. This dis cussion includes various approaches to agriculture- referred to as carbon farming, regenerative agriculture, farming for soil health, and farming forsoil carbon sequestration-and theirpotential to increase agriculture's role as a greenhouse gas (GHQ sink and reduce its role as a GHG source. GHGsinks remove and store GHGs from the atmosphere, and GHGsources emit (release) them. Figure I. Carbon Cycling in Agricultural Soils Source: Figure created by CRS. A iulue A GCH G {rean ik According to the Environmental Protection Agency (EPA), the agriculture sector is a net emitter ofGHGs; agricultural practices, including crop and livestock operations, currently emit more GHGs than they remove. The EPA's annual Inventory ofUS. Greenhouse Gas Emissions andSinks reports estimates of anthropogenic GHG emissions and sinks in the United States,using internationally standardized sectors. On the source side, the agriculture sector's GHG emis sions -primarily methane and nitrous oxide-include those fromlivestockand soilmanagement. The 2020 Inventory shows that in 2018, the agriculture sector contributed about 10% of total U.S. GHG emissions. The Inventory reports estimates of net emissions (emissions minus removals) fromthe Land Use, Land-Use Change, and Forestry sector (LULUCF)-primarily carbon dioxide (C02) emissions and carbon storage. LULUCF includes net emis s ions for fores tlands, agricultural croplands, grasslands, andother land types. Data from2018 and prior years indicate that U.S. croplands are a net GHG source and grasslands area netsink. Land-use change, rather than land use, largely shapes these p atterns-the conversion of other land-usetypes to croplands (netemissions) and to grasslands (net removals). AgrkcLdtural Practces That Store Carbn Soils store carbon in two basic forms: organic (derived fromliving material, such as plant roots) andinorganic (derived fromnonliving material, such as minerals). Soil organic carbon (SOC) measures the carbon in soil organic matter (SOM), which consists largely of soil microbes (i.e., bacteria and fungi), and decaying and decayedplant and animal material. In addition to its role sequestering carbon, SOM is important to soil health and agricultural productivity. Photosynthesis, decomposition, and respiration are themajor factors in determining SOC levels (Figure 1). Photosynthesis fixes atmospheric CO2 into plant material, which can lead to increased SOC. Decomposition of SOM releases CO2 into the atmosphere and leaves a small amount ofcarbonin the soil. Respiration of plants and microbes releases CO2 into the atmosphere as a by- product ofusing organic materials for energy and growth; this process returns to the atmosphere some of the carbon fixed through photosynthesis. Agricultural practices have generally increased net GHG emissions, but certain practices can reduce GHG emissions in the atmosphere andincreasenet carbon storage in soils. Such practices generally reduce soil exposure to air and increase plant root growth. These practices include no-till or reduced-till land management and use of cover crops, compost, and manure. The combination of multiple practices may further increase carbon storage in soils. The adoption of carbon-sequestering practices depends on factors that include requirements for equipment and labor and vary widely in the United States (Table 1). Table I. Selected Carbon-Sequestering Management Practices in Use in U.S. Croplands (2017) Acres % of Total Management Practice (millions) Cropland No-Till (includes Rotational Till) 105 27% Reduced-Till 98 25% Cover Crops 15 4% Source: USDA, 201 7 Census ofAgriculture (COA), 20 19, Table 47. Note: Total U.S. cropland =396 million acres (COA,Table 1). Sc, ntific D a The carbon sequestration potential of agricultural soils has been an active research area for decades. Some scientists are optimistic and others advise caution when considering agriculture's potential to measurably mitigate global GHG emissions. The utility and effectiveness of mitigating GHG emissions via agriculture depends in part on the carbon-storage potential of agricultural soils, carbon-storing potential ofagricultural practices, and carbon storage over time. Carbon-storage potential of agricultural soils. Recent estimates suggest that over the past 12,000 years,human \ Q xa S yg

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