Biopriming with Bacillus subtilis Enhanced the Sulphur Use Efficiency of Indian Mustard under Graded Levels of Sulphur Fertilization

This study investigated the effect of bioinoculants (Bacillus subtilis and Pseudomonas fluorescens) as biopriming agents under varied sulphur (S) fertilizer levels (0, 20, 30, and 40 kg S ha−1) to enhance sulphur use efficiency (SUE) in Indian mustard. The experiment was conducted during the 2018–19 and 2019–20 winter seasons at the research farm of the Institute of Agricultural Sciences, Banaras Hindu University, Varanasi (25°26′ N, 82°99′ E). A randomized block design was employed to assess the combined effect of biopriming and S fertilization on the partitioning of S in different parts of mustard plants, S uptake, SUE, and soil urease, dehydrogenase, alkaline phosphatase, and arylsulphatase activity. Results showed that the application of S fertilizers along with biopriming significantly increased the S content, uptake, and SUE by plants and enzymes involved in the S mineralization process. Application of 40 kg S ha−1 + B. subtilis resulted in the highest S content in the root (0.12%), stover (0.30%), and seed (0.67%), and the highest total S uptake (2.97 g m−2 in the first year and 3.37 g m−2 in the second year), agronomic use efficiency (8.80 g g−1), apparent S recovery (22.37%), urease activity (156.68 µg NH4+ g−1 hr−1), dehydrogenase activity (42.80 µg TPF g−1 24 hr−1), and arylsulphatase activity (39.94 µg pNP g−1 hr−1). However, the highest alkaline phosphatase activity (129.17 µg pNP g−1 hr−1) was found in the treatment that received 40 kg S ha−1 + P. fluorescens. Further, the different indices of SUE revealed that the effect of biopriming was more prominent in apparent recovery efficiency than agronomic SUE and physiological SUE. Conclusively, the present study demonstrated that seed biopriming with B. subtilis along with S fertilization is more rewarding and can promote sustainable production of Indian mustard.