Cover crops can lower crop yields, study shows

Cover cropping as currently done in a major U.S. crop-growing region reduces corn and soybean yields, and could lead to indirect environmental impacts from expanded cultivation to make up for the losses. That’s the conclusion of a study by Stanford University, published in Global Change Biology.

20 million acres of farmland analysed

Cover cropping is currently being done on about 5% of fields in the primary corn-growing region of the U.S. In the first large-scale, field-level analysis of yield impacts from cover cropping across the U.S. Corn Belt, the researchers used satellite imagery to look over about 20 million acres of farmland in Iowa, Indiana, Missouri, Ohio, Illinois, and Michigan. They analysed every field that had grown cover crops for at least three years, comparing them to similar fields that had not been planted with cover crops.

Yield declines of 5.5% for corn and 3.5% for soybeans

On average, fields with cover cropping saw yield declines of 5.5% for corn and 3.5% for soybeans. The greater maize yield losses likely reflect the crop’s greater need for nitrogen fertilizer, a chemical that common cover crops also use, and water, which cover crops can deplete ahead of dry growing seasons.

The yield declines equate with a loss of about $40 per acre for corn and $20 per acre for soybeans. That loss, combined with the cost of implementing cover crops – about $40 per acre – makes long-term adoption of the practice challenging, the researchers write.

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Cover crops could still prove beneficial

Despite the sobering findings, the researchers emphasize that cover crops could still prove beneficial to farmers and the rest of society. It could be that the benefits take a while to kick in, and it’s likely that farmers will become better at implementation. More research can help guide that implementation by showing, among other things, how alternatives to rye—the most commonly used cover crop in the U.S. Corn Belt—might result in higher primary crop yields in some regions.

Cover cropping is one way to store carbon dioxide in the soil. The day is coming when most farmers in the developed world will earn money from storing carbon dioxide in their soils, but when and how much? Find out in this article: How to make money from carbon soil sequestration?