Effectiveness of potassium sulfate in mitigating salt-induced adverse effects on different physio-biochemical attributes in sunflower (Helianthus annuus L.)

To assess whether foliar application of K+S as potassium sulfate (K₂SO₄) could alleviate the adverse effects of salt on sunflower (Helianthus annuus L. cv. SF-187) plants, a greenhouse experiment was conducted. There were two NaCl levels (0 and 150 mM) applied to the growth medium and six levels of K+S as K₂SO₄ (NS (no spray), WS (spray of water+0.1% Tween 20 solution), 0.5% K+0.21% S, 1.0% K+0.41% S, 1.5% K+0.62% S, and 2.0% K+0.82% S in 0.1% Tween-20 solution) applied two times foliarly to non-stressed and salt-stressed sunflower plants. Salt stress markedly repressed the growth, yield, photosynthetic pigments, water relations and photosynthetic attributes, quantum yield (F_v/F_m), leaf and root K⁺, Mg²⁺, P, Ca²⁺, N as well as K⁺/Na⁺ ratios, while it enhanced the cell membrane permeability, and leaf and root Na⁺ and Cl⁻ concentrations. Foliar application of potassium sulfate significantly improved growth, achene yield, photosynthetic and transpiration rates, stomatal conductance, water use efficiency, leaf turgor and enhanced shoot and leaf K⁺ of the salt-stressed sunflower plants, but it did not improve leaf and root Na⁺, Cl⁻, Mg²⁺, P, Ca²⁺, N as well as K⁺/Na⁺ ratios. The most effective dose of K+S for improving growth and achene yield was found to be 1.5% K+0.62% S and 1% K+0.41% S, respectively. Improvement in growth of sunflower plants due to exogenously applied K₂SO₄ was found to be linked to enhanced photosynthetic capacity, water use efficiency, leaf turgor and relative water content.