Foliar NK application mitigates drought effects in sunflower (Helianthus annuus L.)

The supplemental foliar application of nutrients is a viable approach to mitigate the drastic effects of water stress on growth and productivity of crop plants. However, the choice of an effective combination of elements is necessary to achieve the desired results. We report the role of foliar applied nitrogen and potassium in improving the drought tolerance of two sunflower hybrids, i.e., Hysun-33 (drought tolerant) and LG-5551 (drought susceptible). The combined effect of NKc was found to be effective in maintaining turgor, enhancing accumulation of osmoprotectants, increasing stomatal conductance and net photosynthesis and reducing the production of reactive oxygen species and resulted in higher yield under water deficit conditions. Foliar spray of NKc also improved the concentration of N (7 %), P (27 %) and K (27 %) in achenes. The exposure to drought stress was observed to be more detrimental at vegetative than reproductive stage. Moreover, Hysun-33 performed better than LG-5551 under both normal and water deficit conditions. To the best of our knowledge, the study provides one of the first reports regarding combined nutrients application to regulate physiological and biochemical mechanisms responsible for improved drought tolerance in sunflower.