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There is more to Cover Crops than Cover

December 7, 2009

When I was first introduced to cover crops, I was under the impression that their only use was to cover the ground and prevent erosion. But over the past few years and various “life experiences”, I’ve come to realize that cover crops are very diverse and have many different uses.

Cover crops are a great way to reduce erosion. When a crop is harvested and the ground is let bare, this ground is more prone to water and wind erosion. If a cover crop is planted, instead of letting the ground be fallow, the cover crop will reduce soil erosion. Plant leaves deflect rain drops and slow them down. Slowing down the rain drops impact on the soil surface reduces the amount of soil that goes into suspension with the water. Also a cover crops roots system helps hold the soil in place. Reducing soil erosion with cover crops also helps reduce the amount of phosphorus that runs into ground and surface water.

A green manure is a type of cover crop that is grown solely to return minerals and nutrients to the soil. Typically either a small grain or legume is planted late summer/fall after a forage or cash crop has been harvested. This cover crop is grown when the fields would normally be fallow. In the spring the cover crop is tilled into the soil. This returns all the nutrients and minerals the plant took up back to the soil. In addition this green manure is full of available carbon and the micro fauna in the soil convert it to organic matter. With the current shift to No-Till farming methods, the typcial use of a green manure needed to change. Many farmers and reserachers have worked on different ways to handle this cover crop as a green manure with out tilling it into the soil. These farmers plant a small grain or legume in the late summer/fall. In the spring they will use a herbicide or a roller/crimper to kill the crop. This crop gets left on the soil surface and slowly breaks down releasing nutrients and minerals back into the soil and helping increase organic matter.

Cover crops are very useful for nutrient management. In Pennsylvania it is recommended for farmers, that want to spread manure in the winter, to have atleast 25% ground cover or an established cover crop. Cover crops help hold the nutrients that are applied in place for the future crop. Cover crops also need nutrients to grow. So for operations with a little excess manure, cover crops provide a great place to apply that manure.

Until I got involved with the dairy industry, I didn’t realize that cover crops could be used as a feed source. Many dairy farmers will plant rye in the fields that had just been harvested for corn silage. Rye will grow in the fall, on warmer winter days, and in the spring. It does not winter kill. This rye is then chopped in the spring and ensiled. Ryelage is a great dairy forage to be added to the TMR (Total Mixed Ration). In addition forage radishes or turnips can be planted in the late summer/fall and grazed in early winter by beef, sheep, and goats. I do not recommend grazing milking animals on turnips or radishes, for fear of tainting the milk. Forage radishes and turnips will winter kill, so early winter grazing is important.

Cover crop fibrous roots and tap roots create pore space with in the soil. These pore spaces help water to infiltrate back into the ground, instead of running off. Also these pore spaces help crop roots grow deeper and reach more nutrients.

Tillage radishes are a new idea. They grow thick, deep taproots which help to alleviate soil compaction and break through plow pans. Tillage radishes grow in the late summer/fall and will die after the first killing frost. When they decompse their taproot leaves large pore spaces and channels for crop roots to grown in. For more information visit

Cover crops can alter the soil temperature. In the fall growing cover crops will keep the soil warmer because the ground is covered and because living roots increase the activity of the micro fauna. But in the spring cover crop residue can keep the sun from reaching the soil surface and this will reduce how fast the soil But over many years as the cover crops help increase the soil organic matter the color of the soil will change. Soils with higher levels of organic matter are darker in color. Darker soils absorb more sunlight and will warm up faster in the spring.

Cover crops help the soil ecosystem. These roots provide living carbon and nutrients to feed the mirco fauna of the soil.  Since cover crops are grown when a field would normally be fallow, the food the roots provide the mirco fauna helps to increase the population and diversity of the soil ecosystem.

Cover crops like canola and camelina are being grown and researched for bio-fuel. These crops can be planted in late summer/fall and then their seeds are harvested in the spring. This seeds are high oil seeds and can be used to make bio-diesel. Currently there is a lot of ongoing reserach in using cover crops for bio-fuel. This is a newer concept and shows great promise.

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