Sulfates Increase the Antioxidant Activity of Cowpea Subjected to Saline Stress

Water scarcity for irrigation presents significant challenges to agriculture. The use of saline water from deep wells can induce salt stress in crops, negatively impacting their growth and productivity. Nutritional management using sulfates has emerged as a promising strategy to mitigate the adverse effects of salinity. Therefore, this study aimed to evaluate the effect of sulfate application as a salt stress attenuator in cowpea plants (cv. BRS Tumucumaque). The experiment was conducted in a greenhouse using a randomized block design in a 2 × 4 factorial arrangement, consisting of two irrigation water electrical conductivity levels (ECw = 0.6 and 4.5 dS m^-1) and four sulfate treatments: no sulfate (control), calcium sulfate, potassium sulfate, and ammonium sulfate. Irrigation with water at 4.5 dS m^-1 reduced the cowpea growth and yield. However, it also stimulated pigment synthesis and the enzymatic activities of catalase (CAT) and ascorbate peroxidase (APX), particularly when combined with calcium and potassium sulfate, respectively. In contrast, ammonium sulfate intensified salt stress, increasing electrolyte leakage and lipid peroxidation in cowpea plants. Leaf Na⁺ concentrations remained stable, while calcium and potassium sulfate increased Mg²⁺ and K⁺ levels, respectively. The Na⁺/K⁺ ratio was lower with the potassium sulfate application. Overall, the application of calcium and potassium sulfates enhanced cowpea performance by alleviating the detrimental effects of salinity on growth, pigment production, yield, and antioxidant enzyme activity.