The U.S. House of Representatives passed major climate change legislation in 2009 to cap carbon emissions and pay farmers who sequester and store carbon in the soil. The Chicago Climate Exchange has established a market for “carbon credits,” where farmers are paid to adopt certain practices believed to sequester or store increased carbon in the soil. The exchange also pays for practices to reduce emissions of other greenhouse gases, particularly methane.

Integrity is critical to these payment systems. Carbon credits are designed to offset very real emissions of greenhouse gases. They must achieve real and permanent increases in soil carbon storage to effectively address climate change. Fortunately, we can substantially influence the amount of carbon captured on land through management of agricultural crops, livestock, soils and plant communities, but are doing so at a fraction of the rate possible.

Current agricultural recommendations to reduce global warming are to farm with no-till techniques, plant grass and trees, “manage” grazing, and capture methane at confinement livestock operations. More and better approaches can greatly increase the carbon captured and emissions reduced. Most approaches also allow farm and ranch land to better withstand effects of global warming.

Plant and root growth. Over 80 percent of carbon in plants quickly returns to the atmosphere as microorganisms digest plant materials. The carbon most likely to remain in soil is from plant roots. Deep-rooted crops and crop rotations with legumes increase deep soil carbon. Cover crops capture carbon during extended growing seasons in the fall and spring. Crops with lots of above-ground growth potentially contribute more carbon to the soil. Water and fertilizer management for optimum plant growth results in more plant materials above and below ground. Soils without compaction allow deeper and more vigorous root growth. A fallow season with no plant growth generates no soil carbon.

Tillage. No-till farming, which leaves a mulch layer of old plants on the soil surface, is the primary recommendation for farmers to capture carbon. However, scientists now say it captures no more carbon than plowing when roots and buried plant parts are measured more than a few inches deep. Plowing and other surface disturbance increase the breakdown of upper soil carbon while exposing soil to erosion. But managing tillage can both reduce erosion and decomposition while increasing soil aeration, water absorption and root growth.

Fertilization. Nitrogen fertilizers emit nitrous oxide when applied to the soil, and their manufacture from natural gas releases large amounts of carbon dioxide. Nitrogen fertilizer also speeds breakdown of soil organic matter, releasing carbon dioxide. Adding fertilizers in the amounts, locations and times needed by crops is a solution. Adding legumes to a crop rotation limits nitrous oxide.

Livestock. Ruminants (cattle, sheep, etc.) emit methane as digestive gases and in manure. Digestive methane can be reduced with higher quality feeds, both in feedlots and while grazing. Controlling feed rations with simple additives can reduce digestive methane. Grazing management to provide higher quality feed, as in intensively managed pastures with mixes of legumes and grasses, also reduces methane production. Pasture-based dairy operations release fewer greenhouse gases from all sources than do confinement, grain-based operations.

Manure. Manure stored in anaerobic lagoons emits methane at high levels. Liquid manure systems generate nitrous oxide when applied to the soil. Manure from pit/slurry systems and deep-bedded livestock buildings emit half as much methane while contributing organic matter to the soil. Feedlot manure, compost and livestock droppings on pasture release few greenhouse gases.

Erosion. Most soil carbon is in the top few inches, so it can be easily lost to water and wind erosion. No-till and other conservation tillage protect the soil surface, greatly reducing soil loss. Small grain crops, cover crops, contour cropping, buffer strips and shelterbelts cover the ground, slow runoff, or break wind speeds. Practices to build soil life increase the “glue” that holds soil particles together so they are less easily moved offsite.

Organics. Organic farming often includes production practices such as cover cropping, crop rotations with legumes, mulching and manure application. Organic farms using a suite of these practices have been found to increase soil organic carbon at twice the rate of conventional farming practices. Energy use in organic systems can be 50 percent lower than for conventional farming systems, including no-till, when both direct and indirect uses are considered, which results in less carbon dioxide emission.

Biomass energy. Biomass materials from agricultural lands have the potential to produce carbon-neutral energy. However, much of each year’s crop residue is required for erosion protection, and considerably more is needed to retain soil carbon. Only high residue crop systems (e.g. 300 bu/ac corn-soybean) provide that protective level of biomass. Perennial biomass crops, however, might be harvested at greater rates. In addition, production, transportation and processing of biomass may significantly affect the carbon balance of the resulting energy supplies.

Adding Charcoal to Soil. Biochar (charcoal or terra preta) is a form of organic carbon found in many soils that can last for thousands of years. Controlled charcoal production may permit sequestration of more carbon for longer periods. Biochar has been used in Japan for decades as a soil fertility amendment. The “biogas” released in charcoal formation can be captured and used as a fuel source, typically for heating.

Carbon sequestration in soils provides numerous other benefits in addition to offsetting carbon emissions and reducing atmospheric CO2 concentration. These are truly win-win benefits: the practices and results of capturing carbon in the soil improve air quality, water quality, soil quality and biological diversity while making terrestrial ecosystems more resilient to the damaging impacts of global warming. Not least among these effects is the increased ability of agricultural systems to continue to produce food for human use.

Coming Soon: This article is derived from a Center for Rural Affairs report on agriculture and carbon sequestration that will be available shortly. In next month’s newsletter we will share our policy recommendations from the report. For more information, contact Wyatt Fraas, wyattf@cfra.org or 402.254.6893.