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Cover crops prevent erosion, prevent nitrate leaching

By Jean Caspers-Simmet

Date Modified: 10/10/2012 1:10 PM

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RICEVILLE, Iowa —Tom Kaspar, a research agronomist at the USDA-ARS Lab for Agriculture and the Environment at Ames, has researched cover crops for nearly 20 years.

He shared his insights at a recent Iowa Learning Farms/Practical Farmers of Iowa/Mitchell Soil and Water Conservation District field day at John and Jordan Schwarck's farm near Riceville.

Much of Kaspar's research has been with cereal grain cover crops — rye, oats, winter wheat and triticale.

Kaspar's first work involved how cover crops following soybeans impact erosion. He found that cover crops reduced erosion by 50 percent even in no-till and strip-till because they helped anchor loose residue.

"Cover crops helped more water infiltrate into the ground because they created more root channels," Kaspar said.

Those studies led to research on how cover crops affect nitrogen and nitrogen losses.

"Most soils around Ames are drained, and we see pretty high nitrate concentration in our tile drainage, especially during years like this where we've had a dry summer and we didn't get our normal corn yields, but we put on enough nitrogen for normal yields," Kaspar said. "We have a lot of residual nitrogen."

Row crops grow for about five months, Kaspar said.

"There is a lot of time when nothing is growing," he said. "Those are the times when we lose nitrogen and phosphorus and we have a lot of soil erosion, and we're not building soil organic matter."

Cover crops put something in the ground to take advantage of the warm days to get some of that growth back, Kaspar said. Averaged over 10 years, he found that a rye or oat cover crop reduced nitrogen loss by 50 percent. One year was dry like 2012, and cover crops saved 80 pounds of nitrogen. The nitrogen won't necessarily come out the next year. It's a long-term thing.

"Fields that have been in cover crops for 10 years or more get potential nitrogen mineralization," Kaspar said. "That's the amount of nitrogen that comes out of soil organic matter. It's higher where there have been cover crops long-term."

Kaspar said much of his cover crop research was done with cereal rye in part because he could get it to work every year.

"Sometimes we wouldn't get it planted until Nov. 1, but we still got some growth," he said. "We wanted something we could consistently get established after harvest or aerial seeded at crop maturity."

Aerial seeding at crop maturity works well for cereal grains, but rain is needed after seeding. Planting after corn harvest, works for rye, winter wheat or triticale, but not for oats, which winterkills.

Kaspar seeds one bushel per acre of rye when drilling and increases that by 50 percent if flying it on. He drills oats at 1.5 bushels per acre and increases it to two bushels if flying it on.

It is best to kill rye at least two weeks before planting corn, Kaspar said. That isn't an issue when planting soybeans. He uses glyphosate to kill rye in the spring. Tillage also works, but is a little harder.