Optimizing water management in paddy fields can simultaneously reduce methane emissions and cadmium accumulation in rice

Water management significantly impacts methane (CH4) emissions from paddy fields and cadmium (Cd) accumulation in rice grains through often opposing mechanisms, presenting a complex challenge in optimizing practices to simultaneously mitigate both issues. Through comprehensive field observations across four irrigation regimes over three consecutive planting seasons (i.e., the late rice, early rice, and late rice), along with a pot experiment, we developed an innovative strategy that effectively reduces CH4 emissions and Cd levels while maintaining optimal rice yields. The CTFG treatment—an optimized approach combining controlled irrigation (CI) during rice tillering stage with continuous flooding (CF) during rice grain-filling stage—demonstrated remarkable consistent efficacy over the three seasons. Compared to high-yielding irrigation practice, this regime achieved a 33 % reduction in CH4 emissions and a 42 % decrease in Cd content in brown rice, without compromising rice yield. Furthermore, when benchmarked against specialized irrigation regimes, CTFG outperformed a Cd-minimizing regime by reducing CH4 emissions by 39 % and surpassed a CH4-reducing regime by lowering Cd levels in brown rice by 40 %, while maintaining comparable performance in each targeted area. Mechanistic studies revealed that the tillering and grain-filling stages play pivotal roles in regulating CH4 emissions and Cd content, respectively. CI implementation during tillering stage effectively suppressed methanogen activity while enhancing methanotroph populations, thereby significantly reducing CH4 emissions. Conversely, CF during grain-filling stage decreased soil redox potential and promoted sulfate-reducing bacteria, consequently limiting Cd mobility and its subsequent uptake by rice plants. The results of pot experiments further demonstrated the positive effect of CTFG regime in reducing emissions and cadmium levels, thereby confirming the efficacy of this approach. These findings provide valuable scientific insights for developing more sustainable rice production systems through optimized water management strategies. The CTFG approach represents a significant advancement in balancing environmental protection and food safety concerns in rice cultivation.