Application of Calcium Peroxide for Methane Mitigation in Paddy Fields: Effects of Milk Vetch (Astragalus sinicus L.) Incorporation

Addressing the pressing issue of global warming, sustainable rice cultivation strategies are crucial. Milk vetch (MV), a common green manure in paddies, has been shown to increase CH4 emissions, necessitating effective mitigation. This two-year field experiment assessed the impact of applying calcium peroxide (CaO2), widely used in wastewater treatment and soil remediation due to its oxygen-releasing properties, on CH4 emissions in conventional paddy fields (chemical fertilizer-only) and MV-incorporated fields. The results revealed that in conventional paddy fields, CaO2 application significantly reduced the average CH4 emissions by 19% without affecting rice yield. Compared with chemical fertilizer alone, MV incorporation increased the average rice yield by 12% but significantly elevated CH4 emissions. However, in paddy fields with MV incorporation, CaO2 application significantly reduced CH4 emissions by 19% while preserving the yield benefits of MV. Soil analyses indicated that MV incorporation led to increased soil carbon content and increased mcrA and pmoA gene copy numbers, with elevated mcrA gene copy numbers being primarily responsible for the promoted CH4 emissions. CaO2 application improved the soil redox potential, reducing mcrA gene copies and consequently mitigating CH4 emissions. Overall, CaO2 application can contribute to global efforts to reduce CH4 emissions while supporting rice productivity.