More DMPP Is Not Always Better for Mitigating N ₂ O

ABSTRACT

Aerobic composting of food waste for field application is considered a low‐carbon agricultural management practice relative to conventional farmers' practice, however, it poses a risk of exacerbating N ₂ O emissions, particularly in subtropical acidified vegetable soils. The nitrification inhibitor DMPP (3,4‐dimethylpyrazole phosphate) can mitigate this issue, but its efficacy is contingent upon application rates and specific soil‐climate conditions. We conducted a two‐season field experiment with pakchoi and swamp cabbage in subtropical China to evaluate the effects of two DMPP application levels on soil nitrogen (N) availability, crop N uptake, yield, and N ₂ O emissions under partial substitution of chemical fertilizer N with food waste aerobic compost (FWC) N. Five treatments were established: no N control (CK), conventional chemical fertilizer N (CF), 30% chicken manure N + 70% CF (MF), 30% FWC N + 70% CF (FWF), and FWF supplemented with DMPP at 2% or 5% of total CF N applied. Over the two seasons, cumulative N ₂ O emissions from the CF treatment reached 21.0 kg N ₂ O‐N ha ⁻¹ . Both MF and FWF significantly increased emissions, indicating that organic N substitution enhances N ₂ O release. Both DMPP dosages reduced emissions from FWF; however, the 5% dosage excessively inhibited nitrification, limiting nitrate supply and threatening yield. Notably, during the swamp cabbage season, the 2% DMPP treatment maintained yield while increasing leaf nitrate content, aboveground N uptake, and NUE (N use efficiency) by 34.6%, 22.4%, and 17.2%, respectively, and reduced N ₂ O emissions by 29.1%, compared to the FWF treatment. These results suggest that DMPP is not the more the better, a 2% DMPP application, rather than excessive application, is crucial for achieving cleaner and more sustainable nutrient management in subtropical Chinese vegetable fields.