Threshold-window framework reveals management-sensitive controls of CH4 and N2O emissions in flooded rice

Abstract

Rice paddies are major sources of methane (CH 4 ) and nitrous oxide (N 2 O), yet co-managing water and nitrogen (N) to limit both gases remains challenging because emissions arise from non-linear interactions among multiple drivers. We combined a two-year field experiment in subtropical rice, with four realistic water–N treatments (CF/AWD × normal/reduced N), and a two-factor threshold-window framework to summarize these interactions into a few management-relevant states. For CH 4 , key windows were NH 4 + –N × soil water, DOC × soil water, and soil water × temperature; for N 2 O, windows involving mineral N with moisture, DOC, temperature, or pH captured distinct pathways. For most selected windows, especially for CH 4 , the low-emission state occurred when both drivers remained below their respective thresholds, whereas the NO 3 − –N × soil water window for N 2 O showed a crossover pattern. This threshold-window framework condenses complex controls into simple, management-sensitive rules to guide water and N strategies that reduce CH 4 while avoiding large N 2 O pulses in flooded rice.