Optimizing productivity, profitability, and the carbon–energy nexus of the mustard–mungbean cropping system with micronized sulphonated urea

Widespread sulfur (S) deficiency in India is attributed to crop intensification, the use of S-free fertilizers, reduced sulfur dioxide deposition, etc., which is one of the major factors for low oilseed productivity and quality. At present, whatever conventional S fertilizers used by the farmers, exhibit low S recovery (~10%). However, the novel fertilizers like micronized sulfonated urea (MSU), such as sulphonated urea II (US-II), which contains 10% N and 75% S and sulphonated urea I (US-I) contain 40% N and 13% S, with a slow-release nature, have shown potential to improve nutrient use efficiency, soil health, and productivity. However, research on these novel fertilizers is limited, especially with regard to dosage and timing of application and their comparative assessment with conventional S fertilizers on productivity, profitability, and/or on energy, carbon footprints in mustard-mungbean cropping system (MMCS). Therefore, a study was conducted to evaluate MSU (US-I and -II) with ammonium sulfate (AS), bentonite S (BNT), and SSP, applied 100% basal or split (50% basal + 50% as top dressing). The US-II strategic application (15 kg S ha −1 at sowing and 15 kg S ha −1 at 30 days after sowing), significantly ( P = 0.05) improved system productivity (17.14%) followed by US-I (16%), ammonium sulfate (6%) and bentonite S (5.14%) over NPK with no S. This treatment has also enhanced oil content (5.69%), protein content (1.81%—mustard; 1.29%—mungbean) and net returns (mustard; 28.13%; mungbean; 14.16%). Furthermore, carbon output (CO 2 e ha −1 ), carbon sustainability index, eco-efficiency index ($ kg −1 CO 2 e), and energy use efficiency (MJ ha −1 ) were higher under US-II strategic application, which were 15,370, 4.27, 0.49, and 0.17, than without S application, where the values of these parameters were 12,706, 3.38, 0.39, and 0.14, respectively. The CO 2 emission intensity (1.06 CO 2 e kg −1 seed) is lower under US-II strategic application over no-S unfertilized plots (1.28 CO 2 e kg −1 seed). The study concluded that US-II (15 kg S ha −1 at sowing and 15 kg S ha −1 at 30 days after sowing) improved MMCS productivity, protein and oil content, profitability and carbon-energy nexus of MMCS over conventional S fertilizers (ammonium sulfate, bentonite S, and SSP) and S unfertilized plot.