Cover crop contributions to N supply and water conservation in corn production

Abstract Winter annual legume cover crops can reduce nitrogen (N) fertilizer requirements and provide a water-conserving mulch to a subsequent crop. A two-year study was designed to test cover crops of rye (Secale cerealeL.), hairy vetch (Vicia villosaRoth), and big/lower vetch (Vicia grandifloraScopoli) for their ability to produce N and to conserve soil water for a succeeding corn (Zea maysL.) crop. We measured the cover crops' biomass, N yield, carbon (C) to N ratio, and influence on a subsequent corn crop grown under two tillage regimes (disk tillage or no-till). Nitrogen content in cover crop biomass at time of corn planting ranged from 37 to 187 kg/ha. Pure stands of hairy vetch and a mixture of hairy vetch plus bigflower vetch had generally higher N yields, and rye was lowest. Rye growing in association with hairy vetch had lower C:N ratios than rye growing alone. Legume C:N ratios remained generally unchanged from earlier (disked) to later (herbicide) kill dates, but total N and biomass typically increased in the last 2 to 3 weeks before corn planting. Soil water retention was affected by tillage in some cases; no-till was superior to disk incorporation in each case where there was a tillage effect. Cover crops with greater biomass resulted in greater soil water retention. Among cover crops, uptake ofNby corn was greater from hairy vetch or hairy vetch plus bigflower vetch mixture. Biological immobilization of N appeared to be reducing N uptake by corn grown in rye residues. Corn in nonlegume plots fertilized with 140 or 210 kg N/ha took up more N than corn following legumes, but there was no corresponding yield increase. Corn biomass yields following the cover crops ranged from 8.6 to 18.0 Mg/ha with no additional fertilizer N. In the second year of the study, average corn yields following hairy vetch (15.3 Mg/ha) or hairy-bigflower vetch mixtures (16.4 Mg/ha) were not statistically different from corn yields produced by a 140 kg N/ha fertilizer rate (17.4 Mg/ha). These results suggest N from a legume cover crop can replace or substantially reduce fertilizer N requirements in corn production systems in the Appalachian region.