Benefits of cover crops in agriculture include reductions in nitrogen leaching, especially with non-
"Nitrate leaching was clearly reduced when a cover crop was present. The meta-analysis showed a 70% overall reduction in leaching under the non-legume cover crop relative to bare fallow systems...Though a limited sample size, the comparison between legume-fertilized systems and conventional systems showed a significant, 40% reduction in nitrate leaching. Trends in post-harvest soil inorganic N were highly variable. Legume-fertilized systems had post-harvest soil inorganic N pools ranging from 50% below to 80% above conventional systems."
Source: C. Tonitto, M.B. David, and L.E. Drinkwater, “Replacing bare fallows with cover crops in fertilizer-intensive cropping systems: A meta-analysis of crop yield and N dynamics,” Agriculture, Ecosystems and Environment 112 (2006): 58, 66, doi:10.1016/j.agee.2005.07.003.