Cover crops are used to cover and protect the soil. They cover the ground when the regular crop doesn't- usually during the late fall and early spring. Growing cover crops will reduce soil and water losses. Cover crops help after they are plowed under too. The tops and roots of the plants furnish organic matter to the soil when plowed down. If the cover corp contains a legume, some nitrogen is added to the soil.
Wilson, H. A.; Browning, G. M.; and Peterson, J. B.
"Cover Crops Help Save Soil,"
Iowa Farm Science: Vol. 1
, Article 6.
Available at: https://lib.dr.iastate.edu/farmscience/vol1/iss11/6