Cover crop benefits result from the aboveground biomass and roots below the soil surface. Live or dead plant material above the soil surface protects soil from water and wind erosion. Surface material dissipates raindrop energy, which can reduce rainfall runoff, soil erosion, soil crusting and splash dispersal of pest organisms. It also slows wind speeds, thus reducing transport of soil particles.
The surface and subsurface changes that occur with cover crops improve soil moisture by increasing rainwater infiltration and water-holding capacity. In addition, cover crop residues provide an effective mulch that reduces soil-water loss via evapotranspiration. Together these three effects can increase water availability and help reduce the impact of short-term drought on cash crops common across the Southeast.
Cover crops increase soil organic matter and subsequent total soil carbon content, primarily near the soil surface. Increasing soil carbon promotes overall soil health by improving the physical and chemical properties of the soil. Soil aggregate stability is improved, which helps increase soil water infiltration, water-holding capacity and resistance to soil erosion. Soil crusting is reduced, enhancing crop emergence. Decreasing soil strength promotes root growth. Increased biological activity improves nutrient cycling and minimizes the negative effects from disease and pest cycles.
Legume cover crops increase nitrogen availability by fixing atmospheric nitrogen. Small grains “scavenge” residual nitrogen by using the nitrogen for growth, thus immobilizing it in their biomass. This improves nitrogen-fertilizer efficiency, reduces nitrate leaching and helps protect groundwater from nitrate contamination. Reducing erosion decreases the number of soil particles leaving the field with adsorbed plant nutrients, phosphorus in particular.
Cover crops provide early-season weed control via physical mulching and the production of compounds that leach from roots and aboveground residues during their decomposition. These compounds inhibit weed seed germination by providing a natural herbicidal effect against weeds (allelopathy). Cover crops may improve disease management by preventing splashing of pathogen-containing soil particles onto plants. Cover crops may also improve insect management by attracting beneficial insects, especially if allowed to flower.