The promise for American agriculture is enticing: healthier soils, more soil carbon, less fertilizer runoff, and less need for chemicals. The reality of growing cover crops in the off-season — a much-vaunted and subsidized approach to mitigating climate change — is more complicated, according to a new study led by Stanford University. The study, published November 8 in Biology of Global Changeshows that cover crop cultivation, as currently practiced in a major US growing region, reduces corn and soybean yields and could result in indirect environmental impacts from expanded cultivation to offset losses.
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“The use of catch crops is spreading rapidly. We wanted to see how these new practices affect crop yields in the real world outside of small research plots,” said Jillian Deins, lead author of the study and postdoctoral researcher at the Stanford Center on Food Security and the Environment (FSE). at the time of research.
“Farming is a very tricky business and things don’t usually go as planned,” added senior author David Lobell, Director of Gloria and Richard Kushel of FSE and Professor of Earth System Science. “We believe that constant monitoring, assessment and learning is an essential part of truly sustainable agriculture.”
Maintaining vegetation cover on agricultural fields during the off-season can result in significant reductions in runoff and nitrogen seepage into streams and groundwater, reduced soil erosion, and reduced need for weed control chemicals. The practice can also be an inexpensive strategy to keep carbon dioxide out of the air.
Because of cover crop growing’s potential as a solution to climate change and other landscape benefits, the US Department of Agriculture has subsidized the practice with more than $100 million per year since 2016. The Inflation Reduction Act, passed in August, earmarks $20 billion for practices that “directly improve soil carbon, reduce nitrogen losses, or reduce, capture, avoid, or sequester carbon dioxide, methane, or nitrogen oxides emissions associated with agricultural production.” Without these With support, farmers would probably be slower to bear the costs of seeding and digging catch crops. In any case, cover crops are only used on about 5% of the fields in the main growing region for corn in the USA
View fields from space
In the first large-scale, field-level analysis of cover crop yield effects across the US corn belt, researchers used satellite imagery to survey approximately 20 million acres of farmland in Iowa, Indiana, Missouri, Ohio, Illinois and Michigan. They analyzed each field that had had cover crops grown for at least three years and compared them to similar fields that had not had cover crops planted.
Areas with catch crops experienced yield losses of 5.5% for corn and 3.5% for soybeans on average. The greater corn yield losses likely reflect the plants’ greater need for nitrogen fertilizer, a chemical also used by common cover crops, and for water, which cover crops can deplete before dry growing seasons.
The yield declines correspond to a loss of about $40 per acre for corn and $20 per acre for soybeans. That loss, combined with the cost of transplanting cover crops — about $40 per acre — makes long-term adoption of the practice difficult, the researchers write.
Despite the sobering results, the researchers emphasize that cover crops could prove beneficial for farmers and the rest of society. It might take a while for the benefits to materialize and it’s likely that farmers will get better at implementing them. More research can help with this implementation, including showing how alternatives to rye — the most commonly used cover crop in the US corn belt — could result in higher primary crop yields in some regions. Ensuring that cover crop is removed with sufficient lead time before planting primary crops could reduce the likelihood of significant yield losses. Policymakers could encourage cover crop introduction more in areas least likely to experience significant yield losses, such as B. in areas with less vulnerability to water scarcity.
“Learning by doing is really important, and adjustments are almost always needed in terms of both farming practice and government policy,” Lobell said. “The combination of satellite data and powerful machine learning methods can help us make these adjustments with greater flexibility.”