Soil pH Determines Nitrogen Effects on Methane Emissions From Rice Paddies

Rice paddies account for approximately 9% of human-induced methane (CH₄) emissions. Nitrogen (N) fertilization affects CH₄ emissions from paddy soils through several mechanisms, leading to conflicting results in field experiments. The primary drivers of these N-related effects remain unclear and the contribution of N fertilization to CH₄ emissions from the rice paddies has not yet been quantified for global area. This uncertainty contributes to significant challenges in projecting global CH₄ emissions and hinders the development of effective local mitigation strategies. Here, we show through a meta-analysis and experiments that the impact of N fertilization on CH₄ emissions from rice paddies can be largely predicted by soil pH. Specifically, N fertilization stimulates CH₄ emissions most strongly in acidic soils by accelerating organic matter decomposition and increasing the activities of methanogens. Accounting for the interactions between soil pH and N fertilization, we estimate that N fertilization has raised current area-scaled and yield-scaled CH₄ emissions across the total global paddy area by 52% and 8.2%, respectively. Our results emphasize the importance of alleviating soil acidification and sound N management practices to mitigate global warming.