Since wheat harvest is a little ways off, let’s take some time to consider one of the next big things in crop production – Cover Crops. This has become much more than the interest of a “fringe” of crop production (organic farming and sustainable agriculture) and has entered the mainstream with Research and Extension along with the NRCS conducting research and promoting adoption by producers. The actual movement for cover crops really started around forty years ago with the organic/sustainable agriculture movement and has slowly gained acceptance in many quarters. This week, we briefly examine what a cover crop is. Next week examines what the potential benefits are and finally the objective reality of cover crops.
A cover crop may be generally defined as a crop planted primarily to manage soil erosion, soil fertility, soil quality, water, weeds, pests, diseases, biodiversity and wildlife in crop production systems. Some definitions are more precise, more along this line: a crop, usually a legume, planted to keep nutrients from leaching, soil from eroding, and land from weeding over, as during the winter. Finally, the NRCS uses this definition: “A cover crop is grasses, legumes, forbs or other herbaceous plants that are established for seasonal cover and conservation purposes.” In English, a cover crop is a planted when the soil would normally be bare or idle. It may consist of a typical crop plant or something less traditional like tillage radishes, vetches, pea species, sunn hemp, and many others. The cover crop may be terminated chemically, mechanically, or by frost/winter depending on what you planted.  
They are generally planted in the fall for summer row crops and in early summer for winter crops such as wheat. The idea is they will trap nutrients, or even add nitrogen for legumes, and when terminated provided organic matter for the soil. They must be terminated early enough to facilitate adequate soil moisture for the crop to be harvested and to allow for timely planting. Cover crops differ from green manures, which may be considered a type of cover crop, in that a green manure is turned into the soil while actively growing. Typically, a legume is part of the plant mix. The idea is to provide nutrients and organic matter more rapidly than with a traditional cover crop. The difference is that often cover crops are left on the soil surface as part of a conservation tillage program.
What plants can make up cover crops? The list is pretty substantial and numbers over 100 entries by the USDA. A sampling includes winter and spring cereal crops such as wheat, oats, barley, rye, triticale; legumes such as clovers and annual Medicago species (like alfalfa), peas like cowpea and Austrian winter pea, and hairy vetch; grasses like sorghum-sudangrass hybrids or even just sudan grass; and species like turnips, radishes, amaranth species, canola, millets, and even buckwheat. This is just a partial list but you get the idea.  What makes a suitable cover crop varies by region, climate, soil type and soil chemical environment.   
Next week, how do cover crops accomplish all the benefits associated with them.