Mitigating greenhouse gases through conservation cropping and grazing systems
by Sara Berges, Allamakee County Soil and Water Conservation District
With all the talk in the media about greenhouse gas emissions and global climate change, we may be missing discussions about the huge potential soils have for sequestering greenhouse gases. Soil holds three times the amount of carbon dioxide currently in the atmosphere. By increasing soil organic carbon, we can work to offset some of the greenhouse gas emissions caused by our dependence on fossil fuels as well as improve the ability of our soils to handle rainfall extremes.
Soils are natural carbon sinks but need to be managed to function as such. A recent editorial in the Journal of Soil and Water Conservation gives two recommendations for improving the soils ability to sequester greenhouse gases; keeping the soil covered year-round and having livestock out on the land.
Our current system of agriculture is heavily dependent on tillage and chemical inputs to control weeds, pests, and fertility and is a net producer of greenhouse gases. Tillage reduces soil carbon by increasing erosion potential and allowing oxidation to burn off the soil carbon. Since tillage began, most soils have lost 30-75% of their soil organic carbon.
Minimizing tillage and chemical inputs, diversifying rotations, and using cover crops help to reduce soil erosion and increase soil carbon through an increase in the amount of living roots and beneficial microbes and fungi in the soil. These practices also allow rural communities to have better economic and environmental stability due to decreased dependence on chemical and mechanical inputs and increased soil health.
Adding small grains to a corn-soybean rotation has the potential to improve soil health, but has also been found to produce competitive yields and similar (or higher) profits over the rotation when compared to corn-soybean systems.
Research conducted by Matt Liebman and others at the Marsden Farm near Boone has found that three-crop systems that include red clover with the small grain used 80-86% less synthetic nitrogen, 86-90% less herbicide, and half the energy over the entire rotation when compared to the conventional two-crop system. Once the diverse systems were established, they were also more financially stable from year-to-year because they were less reliant on chemical inputs.
Livestock actually produce methane gas, a greenhouse gas, as a byproduct of fermentation. However, when livestock are raised on pastures rather than in confinement, the soil can become a sink for greenhouse gases and offset the gases being emitted, as long as the pasture is not being overgrazed. Rotating cattle through paddocks, called rotational grazing, helps to allow plants time to recover, spreads manure inputs, and reduces compaction. Additional forage for livestock can come from cover crops on crop fields and can help justify the cost of establishment. Not all farmers want to incorporate livestock into their farm operations, but crop farmers could utilize neighbor’s livestock to add additional economic value to their cover crops on top of the soil health benefits.
Soil is a depletable resource, but cropping and grazing practices that build up soil organic carbon can improve soil health and allow the soil to become a sink for greenhouse gases rather than a source. This can be accomplished by keeping the soil covered (through pasture, diverse crop rotations, and cover crops) and integrating grazing livestock into farm operations.
