Skip

News Release

Cover Crops Trap Residual N Following Drought

By Jason Johnson, Public Affairs Specialist

September 2012

This is the perfect year to plant cover crops in Iowa, according to soils and agronomy experts with USDA’s Natural Resources Conservation Service (NRCS). Besides the obvious negative impact on crop yields, the drought will leave residual nitrate in the soil at harvest time, potentially allowing nitrate to leach out the bottom of the root zone.

If more typical precipitation returns in November through April, the amounts of nitrate lost will be much larger this year than usual, leading to nutrient loading to local waters and eventually to the Mississippi River and Gulf of Mexico.

That’s how cover crops can help. Cover crops will scavenge residual N and recycle it through their plant biomass, says Iowa NRCS State Agronomist Barb Stewart. She says as cover crops decompose next year, some of the N taken up by the cover crops will be released for use by the next cash crop, and some will go towards building soil organic matter.

“Fall-planted cover crops would be a good investment this year, to benefit both their own farms and regional water quality,” says Stewart.

The best N-scavenging cover crops include oats, cereal rye, or annual ryegrass mixed with oilseed radish. If a farmer is interested in fall grazing, then turnips or crimson clover could be mixed with the oats and cereal rye.

Stewart says cover crops will help farmers recoup part of their fertilizer N investment from last season, and will improve soil organic matter and soil biological activity. “Cover crops will also be very useful after soybeans for adding organic matter and trapping N released by decomposing soybean residues,” she says.

National soils guru Ray Archuleta recently spoke to six farmer groups in four days throughout Iowa. One of Archuleta’s key messages to farmers is to add living roots to the soil during more months of the year to increase organic matter and improve soil health. Along with eliminating tillage activities, Archuleta touted legume cover crops as natural fertilizers and grasses as scavengers of nutrients often lost after harvest or during winter.

“Diversity above ground improves diversity below ground, which helps create healthy productive soils,” says Archuleta. “Cover crops should be an integral part of a cropping system. They help improve soil health by developing an ecosystem that sustains and nourishes plants, soil microbes and beneficial insects.”

Besides helping to restore soil health, cover crops also protect soil against erosive heavy rains and strong winds. They can provide livestock producers with additional grazing or haying opportunities, and winter food and cover for birds and other wildlife.

Producers are encouraged to check with their crop insurance providers to be sure planting cover crops does not adversely affect crop insurance coverage. Additionally, the Farm Service Agency (FSA) considers grazing of certain varieties of cover crops as harvesting.

If you are interested in planting cover crops, visit your local NRCS office for more information on the best solution for you. Federal, state or local financial assistance may be available.

-30-