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Cover the Soil 24-7
Cover crops are a way for the soil to have a living cover throughout the year. Besides slicing erosion, cover crops can boost overall soil function, such as increased water infiltration.
“We can never talk about soil health until we keep all the soil in the field,” says Terry Taylor, a Geff, Illinois, farmer. Cover crops can prevent soil loss from the 4-inch downpours that are becoming more prevalent, he says.
Like all agronomic tools, though, they work better in some situations.
“Where there are dysfunctional soils, cover crops can make a big difference,” says Newell Kitchen, a USDA-ARS soil scientist based in Columbia, Missouri. “The more degraded the soil and lost soil function, the greater the benefit from using cover crops. Cover crops are great at helping restore soil function.”
Cover crops protect the natural habitat your soil creates. “The ecosystem is not a machine,” says Archuleta. “The soil still wants to be treated like the prairie.”
Covers help provide the diversity similar to the prairie, and they also keep the soil covered the majority of the year.
“Diversity through cover crop mixes gives us a more sustainable system,” says Don Reicosky, a retired USDA-ARS soil scientist from Morris, Minnesota.
Some cover mixes have components that tolerate cool temperatures, while other crops thrive during warm temperatures. This diversity gives microbes the opportunity to munch on carbon throughout the year.
When the price of land skyrocketed, preserving soil wasn’t an option for Les Seiler, a Fayette, Ohio, farmer. He knew he needed to improve it. After no-tilling for 28 years, Seiler decided to take the next logical step in the process; he added cover crops into the equation in 2007.
In Seiler’s corn-soybeans-wheat rotation, cover crops enter into the rotation following wheat.
“I felt soil health could be brought to a new level when I added cover crops,” says Seiler. “Now I’m seeing success from that addition.”
Seiler farms 36 different soil types. His goal is to improve the ground while making poorer soils more uniform. So far, on all 36 soil types, his system of no-till and cover crops has been able to even out the soil, he says.
Organic matter & nutrients
Cover crops also can increase organic matter, a key soil attribute that helps soils better retain water and add nitrogen (N) through increased mineralization. Just don’t expect it to occur overnight. Each percent of organic matter in the soil releases 20 to 30 pounds per acre of N, 4 to 6 pounds per acre of P205, and 2 to 3 pounds per acre of sulfur each year. However, it takes a long time – 10 to 20 years – to build 1% of organic matter, says Kitchen.
Cover crops also recycle nutrients. “Following a drought and in cases where you have nitrate out there, a cover crop is a good option to prevent denitrification and leaching. Cover crops are a good way to mediate nitrate losses, more so than controlled drainage,” Kitchen says.
“If we are going to raise the organic component of our soils, from a soil health program, we have to find a mechanism to pull the N,” says Taylor. “We have to conserve the N we already have in the field.”
Ever try to balance eating salty peanuts with your beverage of choice? The more you eat, the thirstier you get. With your thirst quenched, the more you want to eat. This cycle can go on and on and on.
It’s a bit that way with carbon (C) and nitrogen (N). Soil C provides food for soil microbes. These bacteria and fungi release the ammonium that adds N for a cash crop. Soil microbes thrive at a 24:1 C:N ratio (24 parts C to 1 part N).
“I am a big cover crops person,” says Neal Eash, a University of Tennessee soil scientist. “But some of them can throw the C:N ratio out of whack.”
For example, straw from a rye cover crop has an 82:1 C:N ratio. This forces soil microbes to find more N to accompany the excess carbon. This N has to come from any excess soil-available N. As soil microbes tie up excess N, this could potentially create a soil N deficit until some microbes die and release N via mineralization.
This level can be brought down, though, by adding a hairy vetch cover crop with a C:N ratio of 11:1. Microbes will consume the vetch and leave the excess N in the soil. This surplus N is then available for growing plants.