Can Different Salt Formulations Revert the Depressing Effect of Salinity on Maize by Modulating Plant Biochemical Attributes and Activating Stress Regulators through Improved N Supply?

Salinity is a major constraint in improving agricultural productivity due to its adverse impact on various physiological and biochemical attributes of plants, and its effect on reducing nitrogen (N) use efficiency due to ion toxicity. To understand the relationship between sodium chloride (NaCl) and increased N application rates, a pot study was performed in which the ammonical (NH4+) form of N was applied as urea to maize crops at different rates (control, 160, 186, 240, 267, 293, and 320 kg N ha−1) using two salinity levels (control and 10 dS m−1 NaCl). The results indicate that all biochemical and physiological attributes of the maize plant improved with increased concentration of N up to 293 kg ha−1, compared to those in the control treatment. Similarly, the optimal N concentration regulated the activities of antioxidant enzymes, i.e., catalase activity (CAT), peroxidase activity (POD), and superoxide dismutases (SOD), and also increased the N use efficiencies of the maize crop up to 293 kg N ha−1. Overall, our results show that the optimum level of N (293 kg ha−1) improved the salinity tolerance in the maize plant by activating stress coping physiological and biochemical mechanisms. This may have been due to the major role of N in the metabolic activity of plants and N assimilation enzymes activity such as nitrate reductase (NR) and nitrite reductase (NiR).