Nitrous oxide emissions from maize following grass-clover: Treatment of plant cover and manure with 3,4-dipyrazol phosphate (DMPP) as mitigation strategy

Animal agriculture is a major contributor to greenhouse gas emissions, with nitrous oxide (N 2 O) playing a critical role. In dairy farming, grass-clover (GC) is widely used in crop rotations and often preceding maize, but the period between GC incorporation and maize N uptake has a high risk for environmental losses, including N 2 O emissions. This study investigated if a nitrification inhibitor, DMPP, can reduce spring N 2 O emissions from maize after GC on sandy soil with or without cattle slurry (CS) as supplementary N. The inhibitor was applied to GC before incorporation, together with CS, or both. Emissions of N 2 O and concentrations of N 2 O at 5, 10, 20 and 30 cm depth were monitored during spring in two years. The highest cumulative emissions were observed in the unamended GC+CS treatment (5.1 and 4.2 kg N ha⁻¹ in 2022 and 2023, respectively). N 2 O emissions often occurred at < 60 % WFPS, showing that GC residues and liquid manure created anaerobic conditions sustaining emissions. DMPP application to GC did not significantly reduce N 2 O emissions, possibly due to NO₃⁻ derived from roots. Also, N 2 O accumulation at 20–30 cm was enhanced by CS despite injection to 8 cm depth, suggesting downward transport of NO₃⁻. When applied with cattle slurry, DMPP effectively reduced emissions by an average 71 %, with some treatments even exhibiting net negative emissions. These findings highlight the complexity of soil N dynamics after termination of GC pastures and the importance of management strategies to mitigate this source of N 2 O emissions in dairy farming systems. • Treating grass-clover (GC) with DMPP before cultivation did not reduce N2O emissions. • In contrast, DMPP reduced N2O from cattle slurry added for the following maize crop. • Soil concentration profiles indicated that N2O was mostly produced at 20–30 cm depth. • Nitrate derived from cattle slurry may have supported N2O production in GC residues. • White clover appeared to be more important for N2O emissions than red clover.