Optimizing sulphur fertilization for enhanced energy-carbon efficiency and biological yield of rice-groundnut cropping system

Rice-groundnut is one of the most important cropping systems in Eastern India. Optimization of sulphur fertilization positively affects the energy and carbon balance, contributing to long-term sustainability of the system. An experiment was conducted with the aim of finding energy - carbon efficient and productive sulphur management practices for the system. Five sulphur fertilization strategies for rice (no sulphur, 20 kg S/ha as bentonite, 20 kg S/ha as gypsum, 40 kg S/ha as bentonite, and 40 kg S/ha as gypsum) assigned to main plots, and three sulphur levels (kg/ha) for groundnut (0, 30 and 60) assigned to the subplots were laid out in a split-plot design with four replications during 2021–22 and 2022–23 at Bhubaneswar, Odisha, India. Sulphur @ 40 kg/ha as gypsum/bentonite in rice recorded higher system energy use efficiency (12.83/12.72), energy productivity (6.06/6.01) and energy profitability (11.83/11.72) than other fertilization methods. Application of 40 kg S/ha as gypsum in rice was the most carbon-efficient (system carbon efficiency, 3.59) and had the minimum carbon footprint (0.123 kg C equivalent/kg biomass), keeping 40 kg/ha bentonite S at par. Among the S levels in groundnut, 60 kg/ha was the most energy-efficient, with system energy use efficiency (12.31%), energy productivity (5.86 kg/MJ), and energy profitability (11.31). Carbon efficiency decreased with increasing S levels in groundnut. The combined application of 40 kg S/ha as gypsum/bentonite in rice and 60 kg S/ha in groundnut was the most productive (biological yield: 18.22/18.17 t/ha, respectively) and energy-efficient. Future research should explore low-carbon or carbon-neutral sulphur sources to enhance the system's carbon efficiency.