Effect of Late-Season Drought Stress and Foliar Application of ZnSO4 and MnSO4 on the Yield and Some Oil Characteristics of Rapeseed Cultivars

This study aimed to investigate the effect of late-season drought stress and foliar application of zinc sulfate (ZnSO 4 ) and manganese sulfate (MnSO 4 ) on quantitative and qualitative traits of different rapeseed cultivars in 2 years. Treatments were included two levels of irrigation (normal and drought stress), four levels of micronutrient foliar application (water spraying, ZnSO 4 , and MnSO 4 , separately, and combined application of them), and three rapeseed cultivars (Nima, R15, and KS7). Results indicated that the qualitative and quantitative traits were significantly affected by irrigation, cultivars, and foliar application treatments. The highest seed oil content (43.9%), oil yield (2175.9 kg ha −1 ), oleic acid (62.56%), and linoleic acid (17.25%) were obtained under normal irrigation conditions. Under drought stress conditions, oil quality decreased by increasing the amount of palmitic and erucic acids in all cultivars. Under drought stress conditions, foliar application of ZnSO 4 reduced the erucic acid, palmitic acid, and glucosinolate contents by 9.79%, 7.98%, and 2.80%, respectively, compared to control. Under drought stress conditions and combined application of ZnSO 4 and MnSO 4 , the oleic acid and linoleic acid content were enhanced by 10.07% and 13.24%, respectively, compared to control. R15 indicated the highest yield (5261 kg ha −1 ) under normal irrigation conditions, whereas, under drought stress conditions, the highest yield (3371 kg ha −1 ) was observed in Nima. Therefore, introducing and diversifying rapeseed cultivars is one of the management tools in arid and semi-arid regions to achieve acceptable yield. The quality of canola oil degrades with environmental stresses, and foliar application of nutrients can moderate the effects of drought stress.