|The benefits of cover crops|
|Thursday, February 07, 2013 2:05 PM|
Assistant Professor OSU-Extension Putnam County
Soil erosion and sedimentation are major agricultural problems worldwide. According to Dr. David Montgomery (2012), even if farmers lose soil at the USDA-NRCS acceptable rate of four to five tons/acre/year, they will lose approximately one inch of top soil every 60 years. Montgomery says we are losing 0.5 percent of our arable agricultural soils every year worldwide due to soil erosion and it takes almost 500 years to replenish one inch of topsoil. Cover crops protect the soil by slowing down the wind at ground level. Blowing snow and dirt, also called “SNIRT,” is a common problem on bare or fallow soils. The reduction in sedimentation from water and wind erosion is a huge soil conservation benefit of cover crops (Hoorman, 2008).
Plants and microorganisms are critical in recycling soil carbon, nitrogen, phosphorus, sulfur, and micronutrients. Carbon ties up and stores major nutrients (water, N, P, S) and micronutrients (zinc, boron, copper). A recent study at Piketon, Ohio shows that 65-70 percent of the soil’s carbon originates from plant roots (Aziz PhD thesis, 2011). The soils in Illinois and Iowa are productive because they are high in soil organic matter. Carbon is the key to improving soil productivity because carbon ties up plant nutrients and still makes them plant available.
Increasing crop residue and soil carbon at the soil surface increases water infiltration and soil water holding capacity (Hoorman, 2013). Every one percent soil organic matter holds one to two acre inches of additional water depending on soil texture (Hudson, 1994). Hoorman says, “With the depletion of soil organic matter levels, our soils are becoming harder and denser. Without the continual addition of organic residues from live plants, water runs off the soil surface rather than infiltrating the soil, causing soil compaction and nutrient rich sediment to flow to our surface water. Soil organic matter is needed to improve soil structure so that our soils become more like a sponge, soaking up water and storing soluble soil nutrients” (Hoorman, 2013, pg.23).
Hoorman says “Each soil has a natural ecosystem of diverse microbial species, predators and soil fauna that keep each species in balance. By promoting a healthy soil ecosystem “with cover crops,” many pests are kept in balance and the economic impacts of these pests are greatly reduced” (Hoorman, 2013 pg 23). Hoorman adds, “As mankind starts to rely on manmade solutions like chemicals (herbicides, insecticides, fungicides); resistant weeds, damaging insects, and harmful disease organisms tend to prosper and adapt to render many of these products less effective”( Hoorman. 2013 pg 23). Cover crops promote a healthy soil by increasing the number and species of beneficial microorganisms to compete with or consume these harmful species.
Hoorman says, “Planting a flowering cover crop like buckwheat or a flowering legume crops around the edges of fields improves the population of beneficial insects and may reduce the need for some pesticides” (Hoorman, 2013, pg 24). Cover crops promote mycorrhizal fungus and other beneficial microorganism which inhibit Phytopthora, Rhizoctonia, Phythium, and Fusarium; which are soybean disease causing organisms (Amaranthus and Simpson, 2011). Ground beetles (Carabidae beetles) and lightning bugs (Lampyrida) consume many soft bodied insects (aphids, slugs, caterpillars) which may reduce crop yields. A ground beetle may eat its weight in weed seed or insect larva per day (Altieri et al, 2005). Cover crops compete with weeds for sunlight and nutrients, reducing weed populations and weed seed production. By using chemical inputs less often and only when needed, farmers promote beneficial insects and predators and may extend their useful life so that they do not become resistant to these products.
For more information, sign up for the Cover Crops and Soil Health series being offered at the Putnam County Extension Office from 7-9 p.m. on Monday, Feb. 20 and 25. Cost is $20 for refreshments, handouts, and a Cover Crop Field Guide. Tickets for the Putnam County Pork Banquet at 6:30 p.m. on Feb. 18 at Kalida K. C. Hall are $10 at our office.