Soil Carbon

Carbon is the organic content of the soil, generally in the partially decomposed vegetation (humus) both on the surface and in the upper soil layers, in the organisms that decompose vegetation (decomposers), and in the fine roots. As the Congressional Research Service describes, the amount of carbon in soils varies widely, depending on the environment and the history of the site. Soil carbon accumulates as dead vegetation is added to the surface and decomposers respond. Carbon is also “injected” into the soil as roots grow (root biomass increases). Soil carbon is also slowly released to the atmosphere as the vegetation decomposes. However, opportunities exist to improve soil management in order to increase carbon sequestration.

In the United States, soil carbon sequestration already plays an important role in the carbon cycle. Four main pathways can enable resource managers to increase the impact of soil carbon management:

• Increased soil stability by minimizing soil disturbance.
• Increase plant and animal inputs.
• Improve diversity and number of soil microbes. 
• Provide living cover for soils. 

As Nature4Climate reports, about 10% of the earth’s land area is intensively cultivated to produce crops. Most agricultural soils have lost a large fraction of their original soil carbon, and there is considerable potential to restore this through better management. More efficient use of fertilizers can also have a large impact on global emissions of nitrous oxide, another of the six principal greenhouse gases. Chambers et al. suggest that soil restoration and best practices in rangeland management can yield tremendous carbon sequestration benefits in the United States.

From avoided grassland conversion and reforestation to conservation agriculture and variations in grazing feed, stocks, and intensities, numerous pathways provide potential to improve soil carbon sequestration on working agricultural lands to achieve emission reductions objectives. By identifying carbon mitigation management opportunities across biomes, land trusts can connect emerging best practices to long-standing stewardship approaches to further conservation objectives locally that yield critical global carbon reduction achievements.

Learn More

• A Lifecycle Model to Evaluate Carbon Sequestration Potential and Greenhouse Gas Dynamics of Managed Grasslands
• Carbon Farm Plans, Marin Carbon Project
• Agriculture, Climate Change and Carbon Sequestration, ATTRA—National Sustainable Agriculture Information Service
• Effects of Organic Matter Amendments on Net Primary Productivity and Greenhouse Gas Emissions in Annual Grasslands
• Impacts of Organic Matter Amendments on Carbon and Nitrogen Dynamics in Grassland Soils
• Nature4Climate – Grasslands and Agricultural Lands