Soil Potassium Application Ameliorates Drought-Induced Seed Yield Loss and Enhances Nutritional and Seed Oil Quality in Sesame (Sesamum indicum L.)

Sesame is a considerable oilseed crop, but its growth and production are restricted by drought. Potassium (K) is well known for its mitigating effects against drought. Here, two consecutive years of experiments were conducted with varying K fertilizer rates (0, 60, and 120 kg K2O ha−1) under well-watered and drought conditions to evaluate the impacts of K on sesame seed quality. The results demonstrated that, compared to well-watered conditions, drought caused a decline in seed oil content (5.9–8.6%) but inversely induced an increase in seed K (8.5–23.8%), lignans (10.2–21.6%), and essential amino acids over a period of 2 years. Potassic fertilizer significantly increased seed K, oil, and lignans contents, aligning with ameliorative oil and protein yield relative to K deficiency plants under drought. Moreover, K supply (especially 120 kg K2O ha−1) increased proline and tryptophan contents by 5.2% and 4.9% under drought compared to the plants without K application, which contributed to producing lignans and enhancing the capacity against oxidative changes. Under drought, 60 and 120 kg K2O ha−1 application significantly increased linoleic (5.5–9.3%), and stearic acids (7.1–13.7%) content while decreasing palmitic (5.3–14.7%), oleic (4.6–6.4%), and linolenic acids (4.8–11.9%) content, respectively, thereby increasing the ratio of unsaturated to saturated fatty acids and unsaturation index compared with control without K. Overall, K application at the rate of 120 kg K2O ha−1 could be considered as a practical and straightforward strategy to improve the quality of sesame seed products by increasing seed K, oil, lignans, linoleic acid, and unsaturated index for pharmaceutical and food purposes in areas encountering drought stress.