Urea and potassium nitrate synergy in sesame cultivation: boosting growth, yield, and antioxidant resilience through tailored nitrogen fertilization

This study aimed to evaluate the effects of different nitrogen sources on sesame (Sesamum indicum L.) growth, yield, and physiological parameters to identify optimal fertilization strategies for maximizing production. Sesame is a valuable seed plant known for its oil, protein, and antioxidant content. A two-season field experiment (2021 and 2022) was conducted to investigate the impact of eight nitrogen sources, applied at 126 kg N/ha, including two organic sources (urea and thiourea), four nitrate salts (sodium, potassium, calcium, and magnesium nitrates), and two ammonium salts (sulfate and citrate). The experiment followed a completely randomized block design with three replicates. Among the nitrogen sources, urea exhibited superior performance in promoting vegetative growth, nitrogenous compounds, and seed yield. K nitrate emerged as the leading source for enhancing K⁺ and NO₃^- concentrations, capsules number, and oil content. Implementing Na nitrate increased catalase and ascorbate peroxidase activities, while urea enhanced glutathione reductase activity, and Mg nitrate stimulated glutathione-S-transferase activity. Moreover, Mg nitrate demonstrated the highest efficacy in improving Chl b levels and photosystem II photochemical efficiency. Consequently, K nitrate and urea can be considered optimal fertilizers for maximizing sesame production. Although urea resulted in the greatest vegetative growth of sesame, ammonium salts (citrate and sulfate) exhibited the second-highest effectiveness in enhancing most of the evaluated parameters. Compared to the least effective nitrogen source, urea significantly increased Chl b (57.1% vs. K nitrate), carotenoids (58.8% vs. Mg nitrate), amino acids (31.6% vs. K nitrate), nitrogen content (208.8% vs. ammonium citrate), seed yield (62.8% vs. thiourea), and oil production (41.1% vs. ammonium citrate). These results demonstrate that urea and K nitrate are optimal nitrogen sources for maximizing sesame growth and yield, providing farmers with targeted fertilization strategies to enhance productivity and sustainable nutrient management.