Broadcasting cover crops at corn harvest can maximize biomass and reduce nitrogen leaching

Abstract

Mitigating nitrogen (N) leaching from agricultural fields is critical for improving water quality in the Chesapeake Bay Watershed. Because N mineralization continues after corn (Zea mays L.) uptake ceases, losses may occur between harvest and cover crop (CC) establishment. The objectives of this study were to identify effective establishment methods and CC species for N uptake and biomass production; determine whether planting at harvest enhances N scavenging compared to delayed planting; and assess impacts on corn yield. Four seeding methods were evaluated: (1) broadcasting with incorporation at corn harvest, (2) broadcasting without incorporation at corn harvest, (3) broadcasting with incorporation four weeks post-harvest, and (4) drilling four weeks post-harvest, using cereal rye (Secale cereale L.), hairy vetch (Vicia villosa Roth), rapeseed (Brassica napus L.), and a three-species mix. In Year 2, fall soil nitrate concentrations at 0–15 cm depth in post-harvest treatments (11.4–11.8 mg kg−1) were more than double that of at-harvest treatments (5.2 mg kg−1), with at-harvest incorporated rye showing the lowest winter nitrate (1.7 mg kg−1). At-harvest mix and hairy vetch accumulated the most N in aboveground biomass (181–208 kg ha−1). Year 1 corn yield increased following at-harvest hairy vetch (11,022–11,384 kg ha−1) and incorporated mix (11,587 kg ha−1) compared to the control (8895 kg ha−1), though not in Year 2. Incorporation did not significantly affect outcomes compared to non-incorporated treatments. Planting CCs at corn harvest maximized N accumulation, biomass, and nitrate reduction, offering a practical strategy to mitigate N leaching.