Optimization of nitrogen regulates the ionic homeostasis, potassium efficiency, and proline content to improve the growth, yield, and quality of maize under salinity stress

Salinity has become a global problem for sustainable agriculture and poses a major threat to food security and crop productivity. Adequate nitrogen (N) application is considered an important and economical means to address the issue of salinity stress by alleviating its adverse effects on plant growth. For this, a pot study was performed to investigate the interactive effects of different levels of N and salinity on the morphological, biochemical, yield and quality attributes of maize. For this purpose, seven different levels of N were applied: 0 (control), 160, 186, 240, 267, 293 and 320 kg N ha⁻¹. These treatments were tested both under non-salinized conditions and in the presence of 10 dS m⁻¹ NaCl-induced salinity. The results showed that all parameters improved during the growth period of the maize plantwhen the N dose was increased upto the N5 (293 kg N ha⁻¹) and then followed a reduction trend at the N6 (320 kg N ha⁻¹), which could be due to the late plant maturity. It was also found that Na: K ratio and proline content decreased with increasing N level increased. This could be due to the antagonism of sodium ions (Na⁺) with the ammonium (NH₄⁺) form of N, resulting in improved total K uptake (TKUP), K harvest index (KHI), potassium yield efficiency (KYE), potassium use efficiency (KUE) and physiological K use efficiency (PKUE). Similarly, the increased N concentration also increased the protein, oil and starch content. Overall, optimizing N supply, especially at the N5 level, contributed significantly to improving maize plant adaptability to salt stress via regulating the K and proline content.