Managing Nutrients with Cover Crops

Farmers all over the Midwest are looking to cover crops to fill several niches — soil conservation, nutrient management, and production of an extra forage crop. Whether planted in late summer or after fall harvest, now is an excellent time to start researching cover crop applications and seed varieties.

Kevin Shelley, outreach manager for the University of Wisconsin-Madison and UW Extension’s Nutrient and Pest Management program, says farmers are increasingly using cover crops after relatively short-season crops like wheat or small grains. “There’s a lot of interest,” Shelley said. “Adoption of the practice seems to be increasing for the reasons of providing supplemental feed, but also for soil health and nutrient management.”

Getting cover crops planted by late July or early August covers and protects the ground from summer washouts and winter winds. “It can offer substantial soil erosion protection,” says Shelley. Summer annuals like clover offer the additional benefit of fixing nitrogen that will be left in the soil for the following crop — often corn.

“Having a green and growing crop is more desirable than weeds in an otherwise fallow field,” Shelley adds. For dairy farmers, certain cover crops can offer 1 to 3 tons of dry matter per acre that can serve as heifer or dry cow feed. In addition, cover crops add organic matter to the soil. Even if the above-ground portions of the plants are harvested, the plant roots add to the organic profile in the soil.

Midwestern BioAg President Gary Zimmer has advocated the use of cover crops for over 30 years. “I never miss the opportunity to have something growing on my land,” says Zimmer. “Green plants feed soil life, build organic matter, and capture nutrients in their tissues. Those nutrients will not erode, and they are in a form that is linked to biology so it’s easier for plants to access them.”

Many growers choose to put in a cover crop after wheat or a canning crop like snap beans or peas where double cropping with a more conventional crop would be risky. Oats or barley are two good options to plant after short-season crops are harvested in mid-summer.

Legumes, like some clover varieties, can be an option, but Shelley notes that these can be riskier if the weather turns hot and dry. “The cereal grains need moisture to germinate and grow, but they [legumes] are a little more forgiving. They can make up for it a little later in the season.”

In addition to less establishment risk, cereal grains offer the advantage of producing significant biomass as long as they are planted in the right time frame — the last week of July to mid-August. There have been trials with oats and barley and some with triticale. Barley and peas planted together provide more top growth, and with decent conditions, can provide two tons of dry matter per acre at harvest, Shelley said.

Oats and barley often grow until November and continue to produce valuable forage because small grain production is dependent on photoperiod — in the shorter days of autumn, the plants don’t begin the process of producing grain as quickly.

They continue to produce sugars and don’t go into a rapid decline in quality. That is especially true with varieties of oats that are bred for forage use, Shelley adds. Soil conservation and organic matter are also improved with the use of cover crops. The value of organic matter is magnified if the crop is plowed down for “green manure.”

Working with a Dane County, Wisconsin, farmer last summer, Shelley helped plant oats and field peas after wheat and then knifed liquid manure into the standing crop. That crop was left on the field to be plowed down this spring.

“That was definitely a very impressive crop, providing a lot of cover. There was all this green biomass waist-high in the field.” In that case, the crop reduces the farmer’s need for nitrogen fertilizer for the following crop.

The use of any variety of cover crop will encourage earthworm growth, which in turn creates micropores that channel water and nutrients into the soil profile. Some farmers prefer cover crops with a number of different species planted together because biodiversity is good for the soil. “The different roots growing in the soil have a lot of different associations with fungus, bacteria, and arthropods that like one species or another,” says Shelley.

Another good time to plant cover crops is right after corn silage removal. Apply manure if available and then establish a cover crop to hold the soil in place over winter, Shelley adds. “Having that cover crop in place lessens runoff and scavenges nutrients.”

At that time of the year, it’s really too late to plant brassicas or legumes, but farmers have had good luck with winter rye. “The earlier it can be planted, the better.” Trials have shown that cover crops sown from September 20 through October 1 are significantly better than those planted around October 10 through October 13 for nutrient management or conservation planning.

 

Getting cover crops planted by late July or early August covers and protects the ground from summer washouts and winter winds.

 

In addition to cover crops holding soil nutrients in place over winter, they can provide 1½ to 2 tons of dry matter per acre when harvested at the recommended root stage in the third week of May.

Midwestern BioAg growers have successfully incorporated cover crops into their rotations for years. “All cover crops have different attributes, and it is important that you choose the right cover crop for your farm,” says Zimmer. “I do everything I can to promote healthy soil life on my farm, and planting cover crops is an essential part of my system.”

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Jan Shepel has over 25 years of ag journalism experience and lives in southwestern Wisconsin.