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Growing Crops to Cover the Soil

By Heidi Johnson, Dane County UW-Extension Crops and Soils Educator

The use of cover crops as a conservation practice in conventional, commodity crop production has been greatly increasing over the last couple of years. Here is a quick run down on what cover crops are and how they are being used in agriculture.

What is a cover crop?

A cover crop is a crop that is grown to protect and improve the soil, rather than for cash sale. Farmers typically plant cover crops after they harvest their cash crop in the late summer or fall.

Why do farmers use cover crops?

Farmers plant cover crops for a variety of reasons but typically at least one of their goals is to protect their soil from erosion. Rain and moving water can dislodge soil particles from fields if there is nothing on the surface of the soil to protect it. Cover crops, as their name suggests, cover the soil surface with leaf growth and hold the soil down with their roots. Losing soil is not only bad for the farmer but phosphorus molecules that are adhered to the soil particles can also lead to surface water degradation, So it is a win-win for farmers and the environment if soil stays where it belongs: in the fields.

Cover crops can also help to scavenge important leftover plant nutrients from the soil to save them for the next crop. Nitrogen is a nutrient that is very important for plant development but it can easily be lost if it is left unused in the soil. Cover crops can absorb leftover nitrogen and hold it like a sponge until it is released as the cover crop decomposes, so it is available for the next cash crop.

And lastly, sometimes livestock farmers will feed cover crops to their animals. Depending on the year, livestock producers may be short of animal feed and cover crops provide an alternative feed for their animals. Cover crops can provide a valuable feed source for animals.

What types of plants do farmers plant for cover crops?

Farmers use a wide variety of plants for cover crops but the most common ones are grasses like cereal rye, barley or oats. Cereal rye is one of the most widely used cover crops because it can be planted up until mid-late October in southern Wisconsin and can grow in very cold weather. This makes cereal rye one of the only cover crop options to plant after corn or soybeans.

But farmers are also using many different types of clover, including red and white clover, and different types of plants from the turnip family, including oilseed radish and rapeseed. There are radish and turnip varieties that have been bred for their large root that helps to break up soil, specifically to be most effective as cover crops.

If they are so great, why don’t all farmers use cover crops?

One reason is that it can be difficult for farmers to have the time to get them planted. It is fairly easy for farmers to plant cover crops after a cash crop like winter wheat that is harvested in late July or early August, when there is still plenty of warm weather left in the season to plant and grow a cover crop. It is much more challenging to get a cover crop established after grain corn or soybeans because they are not harvested until October or November when there is limited time left for a cover crop to grow.

Another major reason that not all farmers use cover crops is due to the cost. There are very tight profit margins in agriculture and cover crops add another expense that doesn’t produce an immediate return on the investment. Farmers need to make decisions as to what they can afford to use to produce their crops and remain profitable.

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To explore more topics related to cover crops in Wisconsin, visit the Using Cover Crops in Wisconsin website.

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