Optimizing sulfur for improving salt tolerance of sunflower (Helianthus annuus L.)

Soil salinization limit crop yield and deteriorate product quality in arid and semi-arid agroecological regions. Under such conditions regulation of mineral nutrients may help to sustain crop productivity. Therefore, a pot experiment was carried out to identify optimal sulfur level and source for enhancing salt adaptability of sunflower (Helianthus annuus L.). A uniform salinity level of 100 mM NaCl was developed in each pot and then six S treatments viz. S0, control; S1, 20 mg sulfur kg-1 soil; S2, 40 mg sulfur kg-1 soil; S3, 60 mg sulfur kg-1 soil; S4, 80 mg sulfur kg-1 soil and S5, 100 mg sulfur kg-1 soil were applied by using elemental S and K2SO4 as sulfur source. Supplementation of sulfur caused reduction in tissue Na+ accumulation and electrolyte leakage while increase in tissue K+ and Ca2+ with a subsequent increase in relative water content and photosynthetic rate of sunflower. Increasing sulfur levels in the form of K2SO4 depicted linear increase in plant growth and yield attributes up to 80 mg sulfur kg-1 soil beyond which there was decline in these growth characteristics suggesting that sulfur as K2SO4 at 80 mg sulfur kg-1 soil might be optimum in mitigating NaCl toxicity in sunflower.