Varying Effects of K⁺ and NH₄⁺ on Nitrogen Metabolism Attributes in Selected Maize Genotypes under Salinity Stress

Nitrification and ammonification in soil are impacted by salinity. On the other hand, little is known about how various N and K levels affect N metabolism under salt stress. In order to ensure food security, we must implement alternate strategies for salt-affected regions worldwide, as population pressure prevents the cultivation area from being expanded. This study sought to determine whether applying different amounts of N and K could mitigate the detrimental effects of salinity stress on maize's N metabolism. Based on the findings of Study-I, two maize genotypes with contrasting salt tolerance responses, the most sensitive (Pioneer 3335) and the most tolerant (Syngenta 8441) were screened in a pot trial. Using KCl as the K source and ammonium sulphate as the N source, the experiment included seven N and K treatments: T1 = 150 kg ha-1 K + 250 kg ha-1 N (Suggested); T2 = 100 kg ha-1 K + 250 kg ha-1 N+ 100 mM EC; T3 = 150 kg ha-1 K + 250 kg ha-1 N+ 100 mM EC; T4 = 200 kg ha-1 K + 250 kg ha-1 N+100 mM EC; T5 = 100 kg ha-1 K + 300 kg ha-1 N+100 mM EC; T6 = 150 kg ha-1 K + 300 kg ha-1 N+100 mM EC, and T7 = 200 kg ha-1 K + 300 kg ha-1 N+100 mM EC. The findings showed that the growth (root, shoot length, and fresh biomass), physiological (chlorophyll parameters), enzymatic (glutamine synthases and glutamate dehydrogenase), and ionic characteristics in the root-shoot of maize genotypes were all significantly impacted by salinity, N, and K fertilization, as well as their interaction. The greatest reduction in shoot length (47.30% and 44.76%), root length (75.00% and 62.50%), shoot fresh weight (86.73% and 46.60%), and root fresh weight (86.70% and 76.43%) was observed in T7 and T5, where different levels of N and K fertilization were applied under stress. This was followed by a decrease in the contents of glutamine synthetases in roots (70.87% and 57.01%), glutamine synthetases in shoots (30.54% and 35.72%), total glutamine synthetases (46.67% and 47.12%), glutamate dehydrogenase in shoots (93.46% and 94.29%), glutamate dehydrogenase in shoots (85.04% and 88.12%), and chlorophyll (52.31% and 33.88%). The application of N and K fertilization enhanced the N-metabolism by improving various attributes under saline conditions, according to the study's findings. It could also be a useful tactic to produce even salt-sensitive species in saline environments.