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Increasing Organic Matter by Using Cover Crops

Increasing Organic Matter by Using Cover Crops

By Kris R. Ethridge, Resource Conservationist
Natural Resources Conservation Service
Manhattan, Kansas

The threats of drought and high temperatures are major challenges facing agricultural producers in Kansas. The unpredictability of climactic conditions can leave even the most successful producers with a substandard production year. While producers cannot control the weather, research shows ways to increase the efficiency at which soil functions during these times of extreme weather.

Soil organic matter content is a valuable measuring stick for determining how healthy your soil is and how efficiently it will be able to use available water. Organic matter acts like a sponge in the soil. A 1 percent increase in soil organic matter content can hold an additional 19,000 gallons of water per acre.

So how can we build soil organic matter? One commonly used practice is the use of no-till. No-till is an effective way of conserving moisture by increasing residue levels on the surface which in turn cool soil temperatures during extreme hot periods. These residues eventually break down and provide food for the bacteria-dominated soil microbe populations. However, even with a no-till system soil organic matter content may increase very slowly or not at all. One reason for this slow increase is that the bacteria are constantly feeding. They mineralize extricates of other microbes, such as soil fungi. As the bacteria populations become greater and greater, eventually they dominate the soil fungi populations and feed faster than the soil fungi can provide the carbon rich extricates. When this happens, bacteria move to feeding on existing organic matter in the soil. This bacteria-dominated soil ecosystem in turn prevents soil organic matter from being built up in the soil. The solution is to find the missing link to increase the soil fungi populations and feed the bacteria a more steady diet.

Cover crops are proving to be this missing link in the development of soil health. Cover crops provide benefits such as reducing erosion and providing additional residue cover. But their greatest benefit to the soil and a drought-tolerant field may be what is happening under the surface. Cover crops provide active living roots which form symbiotic relationships with fungi. These relationships are crucial to life on the planet.

Different types of mycorrhizal fungi (which actually means fungus root) can be found on almost 90 percent of all plants in the world. Fungi cannot develop their own food so they attach themselves to living roots. The living roots provide carbohydrates to the mycorrhizal fungi which in turn provide nutrients and water from the soil profile to the living root. The fungi then release extricates such as polysaccharides and sugars which feed the soil bacteria. The bacteria in turn supply nutrients to the mycorrizal fungi which can then be provided to the living root. The result is a more balanced ecosystem in which the bacteria populations are being fed at a steady rate and are not consuming existing organic matter in the soil.

Already, research shows that soil organic matter can increase significantly within a short time frame with the use of cover crops in conjunction with a no-till system. This increased organic matter provides armor for the soil during periods of extreme drought conditions like experienced in the summer of 2012.

Mixes of cover crops that consist of warm- or cool-season grasses, broadleaves, and legumes mixed together appear to maximize the quantity and diversity of mycorrizal fungi populations.

For more information on effectively using cover crop mixes to increase organic matter in your fields, please contact your local NRCS office or conservation district office located at your local county USDA Service Center (listed in the telephone book under United States Government or on the internet at offices.usda.gov). More information is also available on the Kansas Web site at www.ks.nrcs.usda.gov. Follow us on Twitter @NRCS_Kansas. USDA is an equal opportunity provider and employer.