Soil Carbon and Agriculture: Payment and Storage Policies

Climate scientists tell us that extreme weather events such as this year’s Midwestern heat and drought are examples of climate changes that will be more common in the years ahead. These changes will affect our agriculture: how much we can grow, where we can grow it, and how profitable our farmers will be. At the same time, agriculture has a role to play in reducing these impacts.

Midwestern agriculture faces recurring heat waves, drought, and severe weather as the climate reacts to increasing amounts of greenhouse gases. Farmers and ranchers can contribute to reducing global warming impacts as well as buffer their crops from heat and drought with a variety of agricultural practices. Targeted policies can encourage these benefits.
Source: Wyatt Fraas
US agriculture contributes 6% of US greenhouse emissions. These emissions are primarily methane from livestock and nitrous oxide from fertilizers. These two gases are 25 times and 300 times more potent than carbon dioxide at trapping heat in the atmosphere.

Agricultural emissions of these greenhouse gases can be trimmed. However a greater opportunity lies in the potential of agricultural soils to pull carbon out of the air to reduce greenhouse gas levels and gain time to reduce overall emissions.

Fortunately, we can substantially influence the amount of carbon captured on land through management of agricultural crops, livestock, soils, and plant communities.

Private organizations have already established a market for “carbon credits,” where farmers are paid to adopt certain practices believed to sequester or store increased carbon in the soil. These markets also pay for practices to reduce emissions of other greenhouse gases. USDA is moving in this direction as well through its cost-share programs and other policies. It may also consider payments for carbon practices.

Integrity is critical to these payment systems. Carbon credits are designed to offset very real emissions of greenhouse gases. Credits must achieve real and permanent increases in soil carbon storage to effectively address climate change.

Current agricultural recommendations to reduce global warming are to farm with no-till techniques, plant trees, reduce fertilizer use, and capture methane at confinement livestock operations. More approaches can greatly increase the carbon captured and emissions reduced.

Most of these enhanced practices also allow farm and ranch land to better withstand effects of global warming. They also provide improvements in air quality, water quality, soil quality, and biological diversity. Perhaps the most important effect is the increased ability of agricultural systems to continue to produce food.

Agricultural Practices

Plant and root growth. Over 80% of carbon in plants quickly returns to the atmosphere when microorganisms digest plant materials. Deep-rooted crops and crop rotations with legumes increase deep soil carbon, which is likely to persist. Cover crops capture carbon during extended growing seasons. Crops with lots of above-ground growth can contribute more carbon to the soil.

Optimum management of water and fertilizer results in more plant materials above and below ground. However, nitrogen fertilizers emit nitrous oxide in the soil, while their manufacture releases large amounts of carbon dioxide. Adding fertilizers in the specific amounts, locations and times needed by crops can limit excessive emissions. Legumes in a crop rotation also limit nitrous oxide emissions when they replace manufactured nitrogen.

Tillage. Optimal tillage management would reduce erosion and plant decomposition, while increasing deep root growth. In contrast, plowing and other surface disturbances increase the breakdown of soil carbon near the soil surface while exposing soil to erosion.

No-till farming, which leaves a mulch layer of old plants on the soil surface, reduces erosion and achieves substantial increases in carbon near the soil surface. But no-till is not suited to all soils. The carbon near the surface can be quickly lost in a few tillage passes. And some tillage practices seem to foster more carbon deep in the soil, below two feet, than no till.

Many farming practices, regardless of tillage, cover the ground, slow runoff, or reduce wind speeds to reduce erosion: use of small grain crops, cover crops, contour cropping, buffer strips, and shelterbelts. Practices that build soil life increase the “glue” that holds soil particles together so they erode less easily.

Livestock. Ruminants (cattle, sheep, etc.) emit methane as digestive gases and in manure. Simple additives can reduce digestive methane in feedlots. Grazing management to provide higher quality feed also reduces methane production. Most manure management, including grazing, produces few greenhouse gases. An exception is anaerobic lagoons, which emit methane and nitrous oxide.

Organics. Organic farms are more likely than nonorganic farms to use combinations of production practices such as cover cropping, crop rotations with legumes, mulching, and manure application. Each practice adds carbon capture, reduced emissions and other environmental services.

Biomass energy. Plant materials from agricultural lands have the potential to produce carbon-neutral energy. But removing biomass could be a problem: 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 provide that protective level of biomass. Perennial biomass crops, however, might be harvested at greater rates than the annual crops now being used.

Policy Recommendations

Build conservation and carbon payment programs that complement each other. Many conservation and carbon management practices achieve the same goals. Carbon practices should not impair other conservation objectives such as erosion control, water quality, and wildlife habitat. Landowners should be allowed to “stack” payments for carbon management with incentives for conservation to achieve these broader benefits.

Prioritize research to guide protocols for carbon payments. Current payments reward a narrow slice of practices while a wide array of practices with proven carbon sequestration potential goes unrecognized. One “silver bullet” solution will not fit the variety of cropping systems, climates, and soils across the country. However, targeted research could tailor systems to meet those requirements.

Protect long-term results of carbon payments. Sequestered carbon should remain in the soil. Initial carbon trading protocols allowed the credit recipient to end the practice after a few years and return the sequestered carbon to the atmosphere. However, current payments do not provide adequate incentive for landowners to enter into long-term agreements.

Provide real “additionality” to carbon payments. Payments for what would have been done anyway waste limited resources. Instead, innovation should be fostered by paying those who have led the way in the past with early adoption. Those who adopt practices that go beyond the norm in carbon sequestration should also be rewarded. Guidelines must determine when beneficial practices become commonplace or when detrimental practices are in decline.

Incorporate agricultural resilience into carbon management. Many farming and ranching practices both capture carbon and reduce the effects of climate change. Increasing soil organic carbon improves crop yields, absorbs more water during storms and stores it longer, resists erosion, and reduces drought effects. We must be proactive to slow global warming but also realistic about dealing with its impacts, which have already begun.

Ensure that bioenergy production works in concert with soil carbon goals. We risk losing carbon from the soil when crop residues or dedicated energy crops are used for cellulosic ethanol and biomass energy production. Biomass harvest also removes the nitrogen in the crop residue. If that nitrogen is replaced by manufactured nitrogen, it will generate additional nitrous oxide emissions. Much more crop residue is required to maintain soil carbon and fertility than to reduce erosion. We need innovative biofuel options, such as limited biomass harvest from Conservation Reserve Program acres timed to minimize damage to wildlife.

This feature is excerpted from our new report of the same title. Contact author Wyatt Fraas to learn how to get your copy.