Agriculture, Soil and Carbon Sequestration

Last week I spent several days in Richmond at the annual meeting of the Virginia Association of Soil and Water Conservation Districts. It is an annual conference that allows us to meet with colleagues at other conservation districts and cooperating agencies. In years past we had speakers from the U.S. EPA and the VA Department of Environmental Quality and VA Department of Conservation and Recreation (our parent agency) talk about changes in programs necessary to meet the U.S. EPA’s pollution diet. The entire Chesapeake Bay watershed is under a federal mandate to reduce sediment and fertilizer runoff into the bay in order to improve water quality. One of the best ways to assure this is through cooperative implementation of farm best management practices that keep soil and fertilizer on the land...not in our streams.

This year a couple of the speeches from our partner agencies touched on climate change and carbon sequestration. Since the President has stated that the greatest threat to the future is climate change that should not be surprising. Tucked into a very dynamic speech given by Jewel Hairston, Executive Director Farm Service Agency was the fact that 52 million metric tons of CO2 equivalents were sequestered each year in the United States through the conservation reserve and other agricultural programs.

The term “carbon sequestration” covers both natural and deliberate processes that remove carbon dioxide (CO2) from the atmosphere or is removed from emissions and stored in the ocean, terrestrial environments (vegetation, soils, and sediments), and geologic formations. Before human interference the natural processes that make up the global “carbon cycle” maintained a near balance between the uptake of CO2 and its release back to the atmosphere. Though the absolute amount of CO2 in the atmosphere is small (currently about 400 parts per million- 0.04%), it has increased over 7% in the past decade.

Terrestrial or biological sequestration of CO2 can be accomplished through forest and soil conservation practices that increase the storage of carbon (by restoring and establishing new forests, wetlands, and grasslands) or reduce CO2 emissions (by reducing agricultural tillage and suppressing wildfires). In the United States, these practices are implemented to meet a variety of land-management objectives. Many of the agricultural practices that will reduce CO2 emissions will also restore and maintain soil health, reduce sediment runoff into our rivers and maintain or improve groundwater recharge.

About 30% of U.S. fossil-fuel CO2 emissions are offset by terrestrial or biological sequestration of CO2. That is huge. Though, only a small fraction of this uptake and storage of CO2 is the result of activities undertaken specifically to sequester carbon. The largest net uptake of CO2 is due to the ongoing natural regrowth of forests that were harvested during the 19th and early 20th centuries. The capacity of our terrestrial ecosystems to sequester carbon is uncertain.

The upper limit, though unrealistic, for terrestrial CO2 sequestration in the U.S. is the amount of carbon that would be accumulated if U.S. forests and soils were restored to their historic levels before they were depleted by logging, cultivation, and development. The U.S. Geological Survey estimated that in the 18th century 39 gigatons of CO2 was sequestered in forests and soils. Scientists estimate that up to a third of atmospheric CO2 was once in the soil and that the soils of the earth have lost 50%-70% of their CO2. Decisions about terrestrial carbon sequestration for the future require careful consideration of priorities and tradeoffs. For example, converting farmlands to forests or wetlands may increase carbon sequestration, enhance wildlife habitat and water quality, but would reduce crop production and food availability. However, sustainable farming practices can increase CO2 sequestration in cultivated lands.

Soil is a living thing. In farming, soil carbon sequestration, transferring carbon dioxide from the atmosphere into the soil, is accomplished by leaving crop residues and other organic solids in the soil, and enhancing soil quality and long-term agronomic productivity by building soil quality. Soil carbon sequestration can be accomplished by management systems that add high amounts of biomass to the soil, cause minimal soil disturbance by utilizing no-till agricultural practices, conserve soil and water, improve soil structure, and enhance soil fauna activity.

Adding organic matter to farmland is good for soil quality and crop yields, both short-term and long-term. Continuous no-till is an efficient way of doing this, though there was a period in 2008 when this was questioned by some scientists, that is the current consensus. Cover crops and manure also help raise carbon levels.

There are several environmental benefits when cropland is enrolled in the conservation reserve program and properly managed through planting grass, trees, buffers and restoring wetlands, just one of them is sequestration of CO2. The Conservation Districts and U.S. Department of Agriculture work with farmers to implement many of these programs that also protects groundwater and helps improve the condition of lakes, rivers, ponds and streams by reducing water runoff and sedimentation. Another benefit is the protection of millions of acres of American topsoil from erosion. In addition, these programs together sequester more carbon on private lands than any other federally-administered program. Yet, according to the Farm Service Agency 50% of farmers remain unconvinced that climate change is happening; nonetheless participate in these programs to enhance their soil quality and protect their water resources. These are benefits we can see with our eyes in real time.