Super nano urea and sulphur nutrition enhance nutrient use efficiency and profitability of greengram for sustainable production

Improving nutrient-use efficiency while maintaining crop productivity and profitability is essential for sustainable greengram. Super Nano Urea (SNU), combined with balanced sulphur nutrition, improve nutrient acquisition and fertilizer-use efficiency while reducing dependence on conventional nitrogen fertilizers. Therefore, a two-year field experiment was conducted during 2024 and 2025 to evaluate different nitrogen, sulphur and foliar SNU management strategies for improving growth, productivity, nutrient uptake, fertilizer-use efficiency and profitability of irrigated greengram. The treatment receiving 100% of the recommended Nitrogen, Phosphorus and Potassium together with 100% recommended sulphur produced the highest seed yield (1305 kg ha − 1 ) and protein yield (314 kg ha − 1 ), exceeding the treatment receiving 75% of the nitrogen with sulphur @ 15 kg ha − 1 and two foliar sprays of SNU @ 8 mL L − 1 by 2.2% and 2.6%, respectively. In contrast, reducing basal nitrogen by 25% and supplementing it with sulphur and foliar SNU increased nitrogen and sulphur agronomic efficiency by 23.3% and 31.1%, respectively, and nitrogen and sulphur partial factor productivity by 23.9% and 32.1%, respectively, compared with 100% recommended NPK + sulphur treatment. Economically, 100% recommended NPK without additional sulphur recorded the highest net returns and benefit ratio, whereas the reduced-nitrogen SNU treatment generated economically competitive returns with substantially greater fertilizer-use efficiency. These findings demonstrate that full recommended fertilization with sulphur is advantageous when the primary objective is maximizing yield, whereas partial substitution of basal nitrogen with foliar SNU can improve nutrient-use efficiency while maintaining comparable productivity. From a farmer perspective, the choice of nutrient management should therefore consider the balance among yield, input costs, profitability and fertilizer-use efficiency. Integrating SNU with balanced sulphur nutrition provides a promising strategy for improving nitrogen-use efficiency and reducing dependence on conventional nitrogen fertilizer in sustainable greengram production.