Fertilization practices for balancing carbon sequestration, emissions and yield in rice-wheat rotation: A...

Intensive fertilization enhances rice-wheat productivity but poses challenges for climate mitigation and soil health. To clarify trade-offs and identify optimal practices, this study evaluated the effects of fertilization practices on soil organic carbon (SOC) sequestration, greenhouse gas (GHG) emissions, and yield. First, 3171 observations from 38 long-term field trials in China were compiled and grouped by fertilization type, method, frequency, duration, and nitrogen level. Next, a multilevel mixed-effects meta-analysis and nonlinear regression were used to quantify the impacts of inorganic fertilizers (IF), organic fertilizers (OF), and inorganic-organic fertilizers (IF + OF). Finally, net global warming potential (NGWP) and greenhouse-gas intensities (GHGI) were calculated to identify optimal fertilization configurations. Findings showed that fertilization enhanced SOC content, with integrated IF + OF application producing the highest relative annual change in SOC (0.84 g kg^-1·yr^-1) and the largest yield gains (45.8 % for rice, 83.91 % for wheat), outperforming IF and OF. Over 49.25 years, SOC increased under IF + OF by 2.05 %, showing durable carbon sequestration. Despite higher NGWP driven by CH4 emissions, convergent GHGI for IF + OF converged with those for IF over 100 years due to long-term SOC sequestration offsets. Optimal practices included 250∼350 kg N·hm^-2 in 2∼3 split applications, coupled with NPK-based organic fertilization for rice and nitrogen-supplemented straw return for wheat, balancing yield and emissions. Long-term adoption >20 years supported carbon sequestration and reduced emissions without compromising productivity. These results hold significant implications for policymakers seeking to design effective strategies to promote IF + OF practices within sustained actionable thresholds, and contribute to agricultural greenhouse-gas mitigation for low-carbon practices in China's rice-wheat rotations.