Properly managed cover crops protect the soil surface from water/wind erosion and remediate soil compaction. Growing plants feed the soil ecosystem by exuding compounds from their roots—sugars, organic acids, amino acids, and more. These materials also glue soil particles together into aggregates, improving soil structure. Decomposed plant residue becomes soil organic matter that provides food for soil organisms—bacteria, fungi, arthropods, and others—and increases the water storage capacity of the soil.
Cover crops can improve soil fertility in several ways. Unused nutrients from the previous crop are taken up by the cover crop, reducing leaching and volatilization losses. Similarly, legumes and their associated bacteria produce nitrogen that can become available to subsequent crops as plant residue decomposes. Deep-rooted cover crops also scavenge nutrients from deep in the soil. These nutrients become available to crops the next growing season as the residue decomposes.
Cover crops often affect pest pressures in the cropping system. Thick plant residue suppresses weed growth on the soil surface, which blocks sunlight and physically slows weed seedling growth. Some covers produce allelopathic chemicals that hinder weed seedling growth; others suppress nematode activity by repelling, confusing, or starving the nematodes. However, some cover crops provide support for diseases and nematodes that are harmful to following crops. Producers must choose a cover crop carefully in order to support the desired cash crop.