Evaluation of biochar applications combined with alternate wetting and drying (AWD) water management in rice field as a methane mitigation option for farmers’ adoption

Biochar application and alternate wetting and drying (AWD) are emerging as promising technologies recommended for reducing CH4 emissions and water consumption in rice cultivation. In this study, we hypothesized that both technologies could be practiced in combination and this could further reduce CH4 emissions and water consumption when compared to practicing alone. The effects of biochar application and its co-application with chemical fertilizer or compost under conventional or AWD water management on CH4 emissions, productivity of rice, water use, and SOC stock, as well as cost and income were investigated. The experiment was carried out in an irrigated paddy field in the central plain of Thailand during both in the wet and dry seasons. Relative to control (CT), biochar application (BI), its co-application with compost (BC) or chemical fertilizer (BF) reduced seasonal CH4 emissions by 40.6%, 29.5%, and 12.3%, respectively. BI and BC significantly (p < 0.05) reduced grain yield by 19.9% and 10.8%, respectively, while BF significantly increased grain yield by 3.70%. In addition, BI, BC, and BF significantly enhanced soil organic carbon (SOC) stock by 21.2%, 21.4%, and 18.3%, respectively. Compared to the CT, higher production costs were found in BC and BF, but the farmer's net incomes were also higher in BF because of its higher grain yield. On the other hand, water management in all amendment treatments under AWD was resulted in the reduction of CH4 emissions by the average of 18.8% as compared to the conventional system. AWD decreased rice yield by an average of 2.29%. It significantly reduced irrigation water use by an average of 11.9%, resulting in reducing production cost for water pumping. The results show that the practice that combined biochar application, AWD and chemical fertilizer are feasible for CH4 emission mitigation, SOC stock increase and irrigation water saving without significant effects on yield and farmer income.