Droughts are expected to worsen and intense storms to become more frequent across much of the country in coming decades as the planet warms, but their impact on agriculture could be blunted if American farmers focus on their roots.
A new study, released Wednesday, examines the benefits of cover cropping—planting soil-enriching plants between crop cycles—and other soil-boosting practices used around the world, with a close look at Iowa, one of the Midwest's top-producing agriculture states. The study determined that farmers could help their land better withstand some of the effects of a warming climate by making their soil more "spongy."
"Spongy soil holds more water," said Andrea Basche, the study's author and a Kendall Science Fellow in the Union of Concerned Scientists Food and Environment Program. "What we found to be the most effective and consistent way to get more porous soil is keeping roots there."
That certain practices help build soil health—including cover-cropping or "no-till," in which farmers refrain from plowing soil—has long been understood in agriculture. But in the American Midwest, where corn and soybeans are the most widely grown crops, few farmers have embraced these practices. As little as 2 percent of growers in the Mississippi River basin plant cover crops, despite evidence suggesting they not only boost yields but also make soil more resilient to increasingly volatile weather.
Basche set out to understand the specific impacts of soil-building practices, in part to make a clear case to farmers and the architects of farm policy.
"I see this as being the first [study] to quantify how some of these simple steps can make a big difference," she said. "Do we understand what the benefit is of healthier soil, and do we understand the practices that can get us there? Those are the questions we tried to answer."
150 Experiments on Six Continents
Basche looked at 150 field experiments across six continents and found that nearly two-thirds showed that soil held water better if any of a number of soil-building practices were used, including cover cropping, "no-till" and rotational planting, among others. Of those practices, she found that maintaining "continuous living cover"—by growing cover crops or perennial crops—proved the best strategy for improving soil's ability to absorb water.
"This improvement is likely related to the creation of continuous root systems in the soil, which contribute to topsoil retention, increased levels of soil carbon, enhanced biological activity, and reduced water loss from runoff," Basche wrote. "This is a novel scientific finding that can help prioritize the practices that help reduce climate risks."
In Iowa, 60 Percent Less Runoff
In Iowa, which struggled through extreme storms and drought in recent years, Basche found that cover and perennial crops could make more water available for absorption by crops — up to 11 percent more — and would reduce runoff by 9 to 15 percent. In drought years, when rain absorption is even more critical, the benefits were greater. Basche's analysis found that in 2012, a year of extreme drought in Iowa, rooted soils had 60 percent less runoff than soils without cover or perennial crops.
While the percentage of Midwestern acres planted with cover or perennial crops may be going up, according to a recent survey, Basche and other proponents of soil-boosting practices say there are still too many obstacles and too few incentives for many farmers to make the change.
"It takes time for farmers to figure out how to plant cover crops," Basche said. "There's a cost to seed and labor. It complicates management. There's no way of getting around that."
Too Much Emphasis on Short-Term Insurance
U.S. Department of Agriculture policies have, for decades, promoted the expansion of soybeans and corn, at the expense of a more diverse mix of crops. Critics say the department places too much emphasis on short-term crop insurance to help farmers in drought or flood conditions, rather than on soil-building practices that could make farms more resilient in the long term.
"We need more perennials in our cropping systems, as the report suggests," said Ferd Hoefner, policy director for the National Sustainable Agriculture Coalition, which has long advocated cover cropping. "Conservation, research and commodity and crop insurance policy reform is critical to making that happen."
A drought in the Plains states this year, growing fertilizer-caused water pollution and recent reports that the "dead zone" in the Gulf of Mexico—caused by nitrogen runoff—has reached its biggest size ever, only underscore the need for policies that promote soil-building practices, proponents say.
"We need to have roots in the soil," Basche said.