Increased N2O emissions by cover crops in a diverse crop rotation can be mediated with dual nitrification and urease inhibitors

Agriculture significantly contributes to global soil nitrous oxide (N2O) emissions. Crop rotation diversification and cover cropping are feasible agronomic strategies to reduce nitrogen losses to the environment. However, input of cover crop residues could potentially increase soil N2O emissions. Dual nitrification and urease inhibitors (NUI) administered after cover crop termination at the time of nitrogen fertiliser addition could reduce emissions, but this has not been widely evaluated in field studies. A 4-year crop rotation study was conducted to determine the effect of crop diversification and use of NUI on N2O emissions, crop yield and N2O intensity. Nitrous oxide flux was measured year-round using a micrometeorological method deployed on four 4-ha fields. Two fields were managed with a conventional crop rotation (CONV) (corn - soybean - soybean) and two fields were managed with a diverse crop rotation (DIV) (corn - soybean - winter-wheat plus cover crops either as 2species mixture under seeded to corn or 4-species mixture after winter-wheat harvest). The effect of a NUI [N(-nButyl) thiophosphoric triamide and Pronitridine] was tested in corn in the fourth year. The DIV rotation resulted in 43 % lower annual N2O emissions when winter wheat was grown instead of soybean and 18-26 % increase in annual N2O emissions for corn. The DIV rotation increased N2O intensity by 15 % in Year 1 and 36 % in Year 4 compared to corn in the CONV rotation. The use of NUI in DIV rotation resulted in 15 % lower total N2O emissions over 3 years of the rotation cycle. The application of NUI resulted in a 19 % reduction in N2O intensity within the DIV rotation, with no observable effect on corn yield. Further research should focus on optimising the N application rates according to NUI use, considering available nitrogen from crop residues and cover crops when integrated into the crop rotation.