Sulfur-mediated strategies for enhanced yield, photosynthetic efficiency and antioxidant activity of mustard in north-western India

Ground frost, sulfur (S) deficiency and intermittent drought are major constraints limiting mustard productivity in north-western India and contribute significantly to the existing yield gap. Therefore, a two-year field experiment evaluated different S fertilizers and application timings for improving S nutrition, stress tolerance, growth, physiology and yield of mustard. Seven treatments were tested: US-I, US-II, ammonium sulfate (AS) and bentonite S (BNT) applied at 30 kg S ha -1 at sowing; split applications of US-I and US-II (50% basal + 50% topdressing); and an S-unfertilized plot. S fertilization significantly improved growth, physiology, antioxidant activity and yield compared with the control. Split application of US-II increased leaf area index (3-9%) and crop growth rate (3-32%) and improved dry matter allocation. Antioxidant enzyme activities, superoxide dismutase (4.71-6.10%), glutathione reductase (6.67-8.89%), catalase (6.50-8.83%) and peroxidase (5.51-6.80%), were significantly higher than in the S-unfertilized plot and conventional sources (BNT and AS). Stress mitigation was evident through higher leaf relative water content (36.5%) and reduced canopy temperature (0.97 °C). Physiological parameters such as net photosynthetic rate (8.33%), stomatal conductance (10%), transpiration rate (9.26%) and water-use efficiency (6.87%) were also improved under US-II split application. US-II split application produced the highest seed yield (21.6% above control), followed by US-II, US-I, BNT and AS, applied at sowing. In conclusion, split application of micronized S through US-II enhances growth, physiological efficiency, antioxidant defense and yield by alleviating S deficiency and improving tolerance to cold and drought stress. • Split application of micronized sulfur (US-II, 50% basal + 50% topdressing) improved mustard growth and physiology. • Sulfur fertilization enhanced antioxidant enzyme activity and stress tolerance under cold and drought conditions. • US-II split application improved dry matter partitioning toward reproductive organs. • Sulfur nutrition enhanced photosynthesis, water relations and antioxidant defense in mustard. • US-II split application produced the highest seed yield (∼22% higher than S-unfertilized).