Nitrous Oxide Emissions Increase Exponentially with N Rate in Cover Crop-Corn Production

Subsurface banding of poultry litter has been identified as an agronomic management technique to reduce erosion and volatilization losses of nutrients to the environment, but the effect on soil N₂O emissions has not been established. Cover crops are also promoted for their ecosystem services, but their impact on N₂O emissions has been inconsistent and not well-evaluated across a range of fertility management regimes. To assess the interactive effects of subsurface banded poultry litter and cover crops in a production setting, we measured annual N₂O emissions for three years in a field trial of corn (Zea mays) in Beltsville, MD, following either winter fallow or mulched cover crops (cereal rye [Secale cereale], hairy vetch [Vicia villosa], or biculture), with four rates of subsurface banded poultry litter (9‑276 kg PAN ha^‑1) and selected contrasts with urea-ammonium nitrate (UAN, 150 kg N ha^‑1) or incorporated poultry litter (67 kg PAN ha^‑1). N₂O emissions increased exponentially with total N input rate (subsurface banded poultry litter+cover crop residue). This relationship differed by cover crop treatment: the model intercept ranged from 0.336‑1.389 kg N₂O ha^‑1 (rye<bare=mixture<vetch; p=0.01,0.29,0.03), and the exponential coefficient ranged from 0.00293‑0.00586 kg N₂O‑N kg^‑1 N (vetch<rye=bare=mixture; p=0.02, p>0.10).  Subsurface banding of poultry litter increased N₂O emissions relative to tillage-incorporation at equivalent rates following hairy vetch or mixture cover crops (by 75.9% or 59.8%; p<0.001), but we did not detect an effect following cereal rye or bare ground. Subsurface banded poultry litter decreased emissions relative to UAN at equivalent rates following the mixture cover crop, but increased emissions following bare ground (by 33.9% or 44.9%; p=0.002). Our results suggest that reducing agricultural N₂O emissions can be achieved by reducing total N rates, including both applied N and cover crop N; however, further work is needed to evaluate application methods as a mitigation strategy.