Nitrogen Use Efficiency in Cover-Crop Based Corn Production.

A gradient of 6 cover crop species compositions, from 100% cereal rye to 100% hairy vetch, preceeded each year of a corn production system in two sites in Beltsville MD from 2012-2014. The residue from these cover crops contained a range of N, from 59.4±2.2 kg N ha^-1 (cereal rye monoculture) to 151.1±4.0 kg N ha^-1 (hairy vetch monoculture). In unfertilized plots, the net supply of N from these residues harvested in the corn grain increased linearly with the proportion of hairy vetch (slope = 31.1±3.7, intercepts = 9.03±3.7, -26.8±2.6 kg N ha^-1 for the North and South sites respectively, p<0.001, R²=0.69). 

In plots fertilized with subsurface banded pelletized poultry litter at 68-81 kg N ha^-1, the highest yields were achieved following cover crops containing >20% vetch residue, while yields following cereal rye were lower (10.4-11.6 ± 0.5-0.6 Mg grain ha^-1; 8.3 ± 0.5 Mg grain ha^-1, p<0.003). Application method of poultry litter affected yield differently on the two sites: on the non-irrigated North site, tillage-incorporation decreased yield relative to broadcasting or subsurface banding (5.3±0.4, 7.7±0.4, 8.0±0.4 Mg grain ha^-1 respectively, p<0.001), while on the irrigated South site, tillage-incorporation and broadcasting both decreased yield relative to subsurface banding (9.7±0.3, 10.3±0.4, 11.8±0.8 Mg grain ha^-1 respectively, p<0.001).