How Does Nitrogen Application Ameliorate Negative Effects of Long-Term Drought in Two Maize Cultivars in Relation to Plant Growth, Water Status, and Nitrogen Metabolism?

Two maize cultivars, Shaandan 9 (S-9) and Shaandan 911 (S-911), were investigated to explore the ameliorating effects of nitrogen (N) addition on their growth, water status, and N metabolism under long-term drought stress (DS). Elevated N rate increased dry matter, grain yield, relative water content, nitrate reductase activity, soluble protein concentration, and concentrations of free proline and endogenous glycinebetaine (main contributors to osmoregulation) of both cultivars under DS than control. The responses under DS were more significant for S-911 than those for S-9, especially at high N rate. Additionally, S-9 maintained greater evaluated parameters than S-911 with no N addition under DS, and these differences decreased with N application. Correlations were more evident among all parameters under DS than those under control. Thus, moderate N plays an evident physiological role in alleviation of DS effects on plant growth by improving water status and N metabolism, especially for drought-sensitive cultivars.