Reduced nitrogen fertilization under flooded conditions cut down soil N₂O and CO₂ efflux: An incubation experiment

Unreasonable water (W) and inorganic nitrogen (N) fertilization cause an intensification of soil greenhouse gas (GHGs) emissions. W-N interactions (W × N) patterns can maximise the regulation of soil GHGs efflux through the rational matching of W and N fertilization factors. However, the effects of W × N patterns on soil GHGs efflux and the underlying mechanism remain unclear. In this study, urea fertilizers were applied to paddy soils in a gradient of 100 (N100), 80 (N80), and 60 mg kg^-1 (N60) concentrations. Flooding (W1) and 60% field holding capacity (W2) was set for each N fertilizer application to observe the effects of W × N patterns on soil properties and GHGs efflux through incubation experiments. The results showed that W significantly affected soil electrical conductivity and different N forms (i.e., alkali hydrolyzed N, ammonium N, nitrate N and microbial biomass N) contents. Soil organic carbon (C) content was reduced by 14.40% in W1N60 relative to W1N100, whereas microbial biomass C content was increased by 26.87%. Moreover, soil methane (CH₄) fluxes were low in all treatments, with a range of 1.60-1.65 μg CH₄ kg^-1. Soil nitrous oxide (N₂O) and carbon dioxide (CO₂) fluxes were significantly influenced by W, N and W × N. Global warming potential was maintained at the lowest level in W1N60 treatment at 0.67 g CO₂-eq kg^-1, suggesting W1N60 as the preferred W × N pattern with high environmental impact. Our findings demonstrate that reduced N fertilization contributes to the effective mitigation of soil N₂O and CO₂ efflux by lowering the soil total N and organic C contents and regulating soil microbial biomass C and N.