Cover Crops, also known as green manures, are defined as all subsidiary crops that are grown in between main crops in a sequence, i.e. those that naturally die off, senesce, or are deliberately killed before planting the main crop. Cover crops are typically nitrogen fixing legumes- such as clover or Alfalfa- that are usually dug into the soil when the plants are still young, before they produce any crop and often before they flower. Non-legume cover crops -such as ryegrass and buckwheat- can also be used to recycle nutrients and reduce leaching of nitrogen into the groundwater whilst simultaneously suppressing weeds(Teasdale and Daughty 1993; Clark 1994; Rannels and Wagger 1997). Cover crops may be intercalary or whole-season crops; in the latter case green matter may be harvested for forage, energy or other purposes in addition to the principal use as a cover crop.
The positive effects of cover crops suggest a promising role in both organic and conventional arable systems. Appropriate selection of cover crop species depends on the growers criteria. Generally, brassica species are relatively easy to establish, but can result in volunteers and potentially disease problems in following crops, whereas legume species tend to be more difficult to establish and are generally slower growing but can increase the nitrogen content of the soil though nitrogen-fixation.
Reference - Clark A.J., Decker A.M., Meisinger J.J. 1994. Seeding rate and kill date effects on hairy vetch-‐ cereal rye cover crop mixtures for corn production. Agronomy Journal. 86: 1065-‐1070.
- Teasdale J.R., Daughtry C.S.T. 1993. Weed suppression by live and desiccated hairy vetch. Weed Science. 41:207-‐212.
- Ranells, N.N., Wagger M.G. 1997. Winter grass-‐legume bicultures for efficient nitrogen management in no-‐till corn. Agriculture, Ecosystems and Environment. 65:23-‐32.