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What are cover crops all about?

Randy Pepin

Cover crops are a current hot topic. Why all the hoop-la? The term “Cover Crop” can be confusing since some people utilize cover crops as pasture, others harvest them for forage, some plant cover crops in a prevent-plant situation, and others just terminate the cover crop and seed the next regular crop. We hear of people planting various combinations of plant species. What is the common thread in this cover crop discussion? The term “Cover Crop” means that we plant something to “cover” the ground during times when we traditionally may not have something growing in our fields such as after harvest of corn silage, soybeans, corn grain, sweet corn, or small grain that is not a nurse crop.

One of the other latest hot topics in agriculture is “Soil Health”. Soil health encompasses many practices including diverse crop rotation, minimal tillage, livestock manure, and cover crops. Recent research indicates that soil is healthier when something is growing in it for as much of the year as possible. Barren or fallow ground does not provide for a healthy soil. Of course, we do not want weeds to take over, so we must control what is growing. Two cornerstones of soil health are livestock manure, a natural output of livestock operations, and cover crops. Is it possible to integrate timely liquid manure incorporation and cover crops in the same system?

Another popular topic is “Water Quality”, what can cover crops contribute to water quality? Reducing soil erosion to minimize nitrogen, phosphorus, and sediment from entering any of our surface waters can be a direct benefit of cover crops. When soil nitrogen leaches, it can contaminate our ground water and/or surface water. Can cover crops decrease nitrogen leaching? Desired results of using cover crops are less wind and water erosion, increased soil organic matter, reduced soil compaction, and less nutrient loss to the environment, all while maintaining or increasing crop yield.

For many dairy farmers, their crop rotation is corn silage and alfalfa with possibly some corn grain. Dairy farmers frequently plant small grains for an alfalfa nurse crop; thus, the small grain functions as a cover crop in the spring and alfalfa becomes the cover crop that fall. In addition to wind and water erosion protection, alfalfa provides biodiversity in the rotation and fixes nitrogen, making established alfalfa an excellent cover crop.

With corn silage, the nominal plant residue left on the soil surface and the relatively early harvest exposes bare ground to the elements for an extended period allowing opportunity for significant wind and water erosion. The greatest opportunity for utilizing cover crops on most dairy farms is after corn silage harvest. With typical late September/early October corn silage harvest, the main fall cover crop options are small grains. Oats, spring wheat, spring rye, and spring triticale will usually grow if we plant them late September/early October. They will not survive winter, eliminating the need to terminate the cover crop. However, in the spring, we lose protection from wind and water erosion and are unable to sequester nitrogen. Other research indicates that most nitrogen leaching losses happen in the spring. Winter cereals have the benefit of providing cover both fall and early spring; however, you must either terminate the winter cereal before planting corn, or harvest it as a forage in late May, delaying corn planting. The most economical and toughest of these winter cereals appears to be winter cereal rye. Winter triticale tends to be more digestible than winter cereal rye, but winter triticale is more expensive and not as winter hardy as winter cereal rye.

Currently, on several farms around Minnesota, my project involves drilling in winter cereal rye immediately after corn silage or soybean harvest. Later in the fall, we inject liquid manure into the growing winter cereal rye. Injecting manure when soil temperature is less than 50° F helps prevent fall nitrogen losses. We terminated the rye about one week before spring corn planting in 2016. The 24” soil nitrate samples we took this spring showed less soil nitrate under the winter cereal rye than with no cover crop. Previous trials using commercial fertilizer have shown reduced nitrogen leaching under winter cereal rye. It appears we could expect similar nitrogen sequestration with winter cereal rye and manure. How did the winter cereal rye survive the injection of the liquid manure? Better than might be expected, provided the injection tool was not simultaneously performing a major tillage operation. Our intent is to see if the winter cereal rye has any effect, positive or negative, on the corn crop. How about the economics? We have to wait for those results. We have two crop years of this project so stay tuned.


July 2016

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