Synchronizing Planting Windows and Nutrient Inputs for Sustainable Soil Microbial Function in Rice Agroecosystems

This study evaluates the synergistic effects of planting dates and nitrogen (N) management strategies on soil fertility and microbial dynamics in a rice-based system under subtropical conditions in Eastern India. Over two years, three transplanting dates (June 15, July 15, August 15) and four N treatments, such as control, fixed-time chemical fertilization (FTCF), SPAD-based real-time chemical fertilization (RTCF), and integrated nutrient management (RTCF+OF) were assessed. The July 15 planting consistently yielded the highest microbial biomass carbon (MBC), reaching 123 mg/kg in 2013 and 116 mg/kg in 2014 at panicle initiation, alongside peak bacterial counts of 29 × 106 and 31 × 106 CFU/g, respectively. RTCF+OF significantly enhanced microbial activity, soil organic carbon (SOC), and fungal populations (up to 22.7 × 103 CFU/g), while maintaining stable soil pH (≈5.9–6.1), compared to FTCF and control treatments. FTCF recorded the highest available soil nitrogen (up to 142 kg/ha), but it was associated with lower microbial diversity. Regression analysis revealed strong correlations between temperature, solar radiation, and microbial responses, emphasizing the role of weather in shaping soil biological processes. These findings underscore the importance of aligning planting schedules with favorable climatic windows and adopting integrated nutrient strategies to optimize soil health. Future research should explore long-term impacts on greenhouse gas emissions, nutrient-use efficiency, and resilience of microbial communities under climate variability. The study offers actionable insights for climate-smart rice cultivation and sustainable soil management in subtropical agroecosystems.