Integrated Soil-Analysis-Based Fertilization, Organically Modified Biochar, and Reduced Tillage Mitigate Nitrous Oxide Emissions and Sustain Maize Productivity

Mitigating nitrous oxide (N2O) emissions while maintaining maize productivity and soil quality is an important challenge for sustainable crop production. A three-year field experiment comprising six cropping seasons was conducted in tropical Thailand to evaluate the effects of soil-analysis-based fertilization (SF), two organically modified biochars—organic acid-soaked biochar (BI-OS) and co-composted biochar (BI-CP)—and selected combinations of these treatments with reduced tillage (RT) on N2O emissions, grain yield, and soil properties. Compared with traditional farmer practice (TP), SF reduced annual direct N2O emissions by 28.1% without a statistically significant reduction in grain yield. The addition of BI-OS to SF further reduced N2O emissions, whereas BI-CP resulted in emissions comparable to those under SF alone but provided greater improvements in soil fertility indicators. Among the tested treatments, SF+BI-OS+RT achieved the greatest N2O mitigation, reducing annual emissions by 46.6%, from 3.52 kg N2O ha−1 under TP to 1.88 kg N2O ha−1, while maintaining maize productivity and reducing yield-scaled emissions. In contrast, SF+BI-CP+RT produced the greatest increases in soil pH, cation exchange capacity, and soil organic carbon sequestration. Overall, integrating SF, organically modified biochar, and RT improved the environmental performance of tropical maize production, with BI-OS providing greater N2O mitigation and BI-CP offering greater benefits for soil fertility.