The response of greenhouse gas emissions, crop yield, and soil health to water scarcity and biochar application in rice cultivation

Projected climate change impacts, such as delayed rainfall and increased drought frequency, threaten rice cultivation and global food security. This study evaluated the effects of water scarcity at critical growth stages and biochar application on greenhouse gas (GHG) emissions, yield, and soil health in Central Thailand using the drought-tolerant cultivar Pathum Thani 1. Treatments included continuous flooding and water scarcity during tillering, reproductive, or both stages, with and without biochar, across wet and dry seasons. Water scarcity significantly reduced methane (CH4) emissions by inhibiting hydrogenotrophic methanogenesis (Methanocella) and acetoclastic methanogenesis (GOM Arc I of Methanosarcinales) but increased nitrous oxide (N2O) emissions via enhanced nitrification. Despite higher N2O emissions, total GHG emissions, expressed as the global warming potential (GWP), were lower under water-scarce conditions than under continuous flooding, with reductions of 27.1%, 43.0%, and 58.1% during tillering, reproductive, and both stages, respectively. Water scarcity during tillering stage maintained yield, whereas water scarcity during reproductive stage caused a significant reduction in yield. Biochar amendment further mitigated GHG emissions, improved yield by 12.2%, and enhanced soil health by increasing soil pH, nutrient availability, and soil organic carbon sequestration. Its high porosity and surface area also suppressed methanogenesis and reduced N2O formation while improving nutrient use efficiency. The strategic use of water restrictions during tillering, combined with biochar, provides a sustainable approach to mitigate GHG emissions, optimize water use, and sustain soil health and productivity. In resource-limited scenarios, prioritizing tillering-stage water scarcity over biochar application is recommended because of its greater GHG mitigation potential.