Long-Term P Fertilizer Application Reduced Methane Emissions from Paddies in a Double-Rice System

Rice is the main staple food worldwide, yet paddy fields are a primary source of artificial methane (CH4) emissions. Phosphorus (P) is a key element in the growth of plants and microbes, and P fertilizer input is a conventional agricultural practice adopted to improve rice yield. However, the impact of long-term P fertilizer addition on CH4 emissions in rice paddies is still unclear. To test this impact, a 36-yr field experiment with and without P fertilizer application treatments under a double-rice cropping system was used in this study to explore how continuous P application affects CH4 emissions and related plant and soil properties. The cumulative CH4 emissions were 21.2% and 28.6% higher without P fertilizer application treatment than with P fertilizer application treatment during the early and late season, respectively. Long-term P fertilizer application increased the rice aboveground biomass by 14.7-85.1% and increased grain yield by 24.5-138.7%. However, it reduced the ratio of root biomass to aboveground biomass. Long-term P fertilizer input reduced the soil NH4+ concentrations in both rice seasons but increased the soil DOC concentrations in the late season. The soil methanogenic abundance and CH4 production potential were similar without and with P fertilizer application treatments; however, the methanotrophic abundance and soil CH4 oxidation potential with P fertilizer application treatment were significantly higher than without P fertilizer application treatment. Our findings indicate that long-term P fertilizer input reduces CH4 emissions in rice fields, mainly by improving CH4 oxidation, which highlights the need for judicious P management to increase rice yield while reducing CH4 emissions.