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About a third of arable land is now moderately to severely degraded, costing the world US$400 billion in agricultural production each year, according to the U.N. Food and Agriculture Organization (FAO). But cover crops offer a potential solution, producing environmental and economic benefits urgently needed by farmers everywhere.
According to Better Soils, Better Lives Founder Roland Bunch, unsustainable farming practices, triggered by population growth, have replaced ancient conservation techniques like forest fallowing in sub-Saharan Africa. “As a result, the organic matter content of the soil has dropped from the normal 4 percent before the 1980s, to less than 1 percent today,” he writes.
Soil organic matter (SOM) can bring invaluable benefits to the soil, including a sturdier soil structure, a higher water retention rate, an enhanced nutrient profile, and strengthened resilience against chemical changes, according to a study in the journal of Environmental Monitoring and Assessment. A lack of SOM is a key indicator of soil degradation.
The use of cover crops is one way to build SOM on farms. Bunch defines cover crops as “plants, including trees, bushes, crawlers, and creepers that fertilize the soil, control weeds, and overcome droughts.” These crops can be grown alongside cash crops or after harvest. Commonly used cover crops, especially grasses and legumes, come in annual, biennial, or perennial varieties.
“We want to think about cover crops as a system that enhances soil biology and its nutrient cycle,” environmental scientist and adjunct professor Katharhy F. tells Food Tank. By adding biomass to the soil, cover crops stimulate trillions of microbes that break down minerals necessary for plant growth, he explains. A meta-analysis published in the journal of Soil Biology and Biochemistry finds that cover crops can increase microbial abundance by nearly 30 percent compared to barren fields.
Some cover crops are scavengers, collecting nutrients left behind from cash crops that would otherwise be lost to erosion. Others attract bacteria that convert nitrogen gas to a usable form for plants.
Cover crops can also serve as crucial carbon sinks. As plants absorb sunlight and convert it to carbon sugars through photosynthesis, the roots feed the microorganisms, which then decompose and store the carbon underground. This is known as carbon sequestration.
According to the Sustainable Agriculture Research and Education Program (SARE) of the U.S. Department of Agriculture (USDA), cover crops could potentially sequester an annual 60 million metric tons of carbon dioxide equivalent when planted on 20 million acres across the U.S. This is analogous to removing 12.8 million passenger vehicles off the road. Further, an eight-year study conducted in Ontario, Canada finds that each tested cover crop variety increased the soil organic carbon content of the soil–some as high as 22 percent–compared to control fields without cover crops.
Bunch adds that cover crops can attenuate the effects of droughts. “According to scientific research carried out here in Malawi, just using [cover crops] well on degraded soils will allow the rainwater infiltration rate to increase from about 15 percent to 60 percent,” he tells Food Tank.
Cover crops also provide physical coverage that blocks out sunlight, retaining the soil moisture and inhibiting the growth of weeds.
These environmental benefits help to support the optimal outcome for farmers: healthier, more robust cash crop yields, even in drought conditions.“I have seen successful cases of major soil fertility improvement among literally thousands of farmers,” Bunch tells Food Tank. In Africa, while results may initially be slow, he emphasizes, “by the third year maize yields should have doubled, and by the sixth year, they should have tripled.”
In addition to generating direct financial gains to farmers, cover crops bring important cost savings. Enhancing soil health “reduces financial liability for environmental conditions,” Katharhy F. tells Food Tank. For example, more stable soils help prevent runoff, leading to a lower risk of punitive costs from water pollution.
A “return of natural capital” also lessens the need for expensive inputs, he says. More nutrients in the soil can help farmers reduce their use of fertilizers, fewer weeds from cover crops may lead to less extensive herbicide application, and greater biodiversity reduces pesticide demand by disrupting pest and disease cycles. Meanwhile, improved soil moisture means erratic rainfall due to climate change poses less economic risk to farmers.
Producers across the world are catching on to these immense advantages. “Over 15 million farmers are using [cover crops],” Bunch says. In the U.S. alone, there was a 50 percent increase in the planting of cover crops between 2012 and 2017, USDA Economic Research Service figures reveal.
Bunch asserts that a lack of knowledge is one of the greatest impediments to utilizing cover crops. It can be challenging to determine which crops work best if resources and expertise are limited. “All we would need is for more organizations to learn about them, find out which systems are needed in each situation, and then train farmers in how to manage them,” he tells Food Tank.
Katharhy F. believes that farmers are in a position to adopt and spread this knowledge. “Sometimes game-changing ideas require timing, and I believe we are in the right time.”
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Photo by Jeremy Bishop, Unsplash
Shelley Rose is a Research and Writing Intern at Food Tank. She earned a BA in political science and a paralegal certificate from Marist College, and is currently pursuing her Master of Food and Agriculture Law and Policy degree from Vermont Law and Graduate School. Shelley is particularly interested in the environmental and public health impacts of the food system.
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