Prioritize for success with cover crops

Wisconsin State Farmer

Wisconsin Dells — Cover crops are plants such as small grains, legumes, brassicas and others that are planted between cash crop seasons to keep a living cover on the landscape. Numerous studies have shown these plants can help protect soil and water quality, reduce chemical input costs, improve farm resiliency, boost yields, increase forage availability and improve wildlife habitat.

In Iowa, the number of cover crop acres has increased dramatically over the past several years — from fewer than 10,000 acres in 2009 to about 300,000 acres in 2013.

Practical Farmers of Iowa has played a central role in bringing about this transformative change to the landscape.

Finding the right cover crop for intended goal can be a challenge as can managing the cover crops once they are established.

Sarah Carlson has been with the Practical Farmers of Iowa for 10 years. Practical Farmers of Iowa is a farmer-led group that does on-farm research and shares the findings with others in the group.  The organization hosts numerous field days and events and also shares the findings of the research on line.

When Carlson spoke to the more than 200 people attending the Discovery Farms conference in Wisconsin Dells recently, she described her work on finding ways to better incentivize the use of cover crops and small grains by farmers.

"Iowa doesn’t have corn silage, small grains or canning company crops, so putting cover crops in a corn/soybean rotation is more of a challenge," Carlson said.

But she believes it is important to find a way to do it.

“Any cash crop that is not followed by living roots is leaky," she said. "When crops are growing, the nitrogen goes into the plant. When there is no crop growing, the nutrients leak out of the soil.”

She said the best approach to getting started with cover crops is to keep it simple.

Stick with the basics

When starting out, using one or two cover crops is an excellent way to get acquainted with their benefits. With lower commodity prices, expensive seed mixes are not necessary. The most popular choices are forage radish and cereal rye.

Carlson pointed to the need to consider the goal before deciding on a cover crop. Then consider other things. What is your crop rotation and harvest timing?  Do you want a cover crop that will over winter?  How will you seed the cover crop?

In Iowa, most farms start with grasses such as rye. Some have brassicas like rapeseed, radish, turnip or mustard, and often they mix grasses and brassicas.

Legumes like the various types of clover or hairy vetch are good, but they need time to develop. 

Carlson shared the results of farmers who used rye as a cover crop and said there are various scenarios for killing off the rye. Letting it grow longer provides a canopy until the crop that has been no-tilled into it begins to develop its own canopy. It can be risky, however, if weather conditions prevent killing it off in time.

The presence of a cover crop also helps to warm the soil in spring, allowing for earlier no-tilling of the row crop. Letting a cover crop get bigger before termination may, at times, take moisture away from the grain crop, but it also helps to build organic matter in the soil and, in turn, the moisture-holding capacity of the soil.

While many Wisconsin farmers harvest rye in spring before establishing corn and feed the rye to their dairy animals, many Iowa farms do not have livestock. Some Iowa farmers find it beneficial to graze the rye in spring before planting corn and terminating the rye.

“If you’re going to graze cover crops," Carlson cautioned, "it will be very important to read the label on your herbicides.”

Carlson also reminded attendees that every year is different.

Farm findings

She also shared the results of various methods used by the Iowa farmers to establish their cover crops. While many Wisconsin farmers establish a cover crop after harvesting corn silage or winter wheat, she said Iowa farmers raising grain have later harvest dates resulting in less time for cover crops to develop before freezing.

Many Iowa farmers have their cover seed flown on after the establishment of corn or soybeans. Some use a high-boy to overseed after the establishment of the grain crop. Some find drilling it in works the best.

Regardless of the method, Carlson said, “Cover crops are cheap asset protection. There is a dollar value to soil and the nutrients in it. If you prevent soil loss, you have save money.”

Looking at the dollar savings by protecting soil, she shows a one-fourth inch soil loss in a year on an acre of land results in 4 tons of soil lost. In a 40-year period of time, that is a 160-ton loss. Considering the land value of 49 cents per ton of soil plus the nutrient loss that comes from erosion, estimated at $5.57 per ton, a farmer will save $6.06 per ton of soil that is kept on the field and not lost to erosion.