Cover crops are plants seeded into agricultural fields, either within or outside of the regular growing season, with the primary purpose of improving or maintaining ecosystem quality. Cover crops have many benefits including:
- Erosion Control
- Weed Suppression
- Improved Soil Fertility
- Plant Disease Suppression
- Insect Pest Suppression
- Improved Soil Health
- Increased Soil Water-holding Capacity
- Improved Water Quality
Cover crops are generally divided into two categories; Legumes and non-Legumes.
Legumes – Legumes such as vetch, crimson clover, Austrian winter peas and others have the ability to add nitrogen to the soil by a process known as fixation. Central Indiana, where our project is located, is on the border for the area where legumes can actually add to soil fertility through this process. The reason is that legumes must first grow to a certain size, produce nodules which contain nitrogen-fixing bacteria, and then begin to add nitrogen to the soil. This takes time and in our area the growing season is often not long enough for this process to really get going. But some years it is and when this happens, farmers can find themselves reducing their fertilizer costs the following year.
Non-legumes – These are, as the name says, any plants which are not legumes. Many of these are grasses such as oats, annual ryegrass, cereal rye, and broadleaves such as the brassicas (oilseed radish), buckwheat and mustard. Grasses are often used when there is nitrogen remaining in the soil following harvest of the cash crop as they are very good at using that nitrogen and storing it where it may be cycled back into the soil for the following year’s crop.
Many cover crops planted are mixes. These enable farmers to take advantage of multiple plant characteristics. While most cover crop mixes consist of two to four species, experienced farmers will sometimes plant mixes containing ten or more cover crop species.
One of the largest concerns with using cover crops is termination. Cover crops are wonderful – until the resources contained in the soil are needed by the cash crop. If cover crops survive past this point, they become a weed. While much research has gone into successful termination, many farmers just beginning to use cover crops select species which are killed by the cold winter temperatures. Oilseed radish and oats are a common cover crop mix for people just starting out.
Cover crops work well in a variety of farming systems. They are often used in no-till but even farmers who perform tillage operations find cover crops very beneficial. A key is to select the correct species to provide the benefits the farmer is looking for. One useful resource for this is the Midwest Cover Crops Council Cover Crop Selector tool.
In addition to providing environmental benefits, many farmers find that planting cover crops can reward them financially. Some farmers have been able to reduce input costs for pesticides and fertilizers. Others have reported yield increases from planting cover crops. Sustainable Agriculture Research and Education (SARE) recently released a report which discusses some of the benefits farmers have experienced through the use of cover crops.
The adoption of cover crops as a management tool has been increasing recently however it is still used on a minority of crop acres in the United States. It is difficult to determine exactly how many acres of US farmland are planted to cover crops but estimates seem to be in the 5-10% range.