Effects of nitrogen fertilizer rates and waterlogging on leaf physiological characteristics and grain yield of maize

Nitrogen fertilizer supply and use play a vital role in determining crop growth and yield. However, the effects of nitrogen fertilizer levels on plant growth under waterlogging conditions remain elusive. The objective of this study was to investigate the effects of nitrogen fertilizer rates (0, 90, 180, 270, and 360 kg N ha−1, designated N0, N1, N2, N3, and N4, respectively) on leaf physiological characteristics and grain yield of maize (Zea mays L.) under two water regimes (WW or well-watered through the maize grown season and WL or waterlogged for six days at the sixth-leaf stage). Overall, in comparison to WW, WL treatment showed a reduction in the following traits, at all nitrogen rates: plant height, leaf area index, SPAD value, superoxide dismutase, peroxidase, and catalase activity, net photosynthetic rate (Pn), transpiration rate, stomatal conductance, ears per ha, kernels per ear, 1,000-kernel weight, and grain yield. Moreover, the majority of the above parameters increased with the increase in nitrogen application rate under WL, as a result of the enhanced available nitrogen content at higher nitrogen application rates. Therefore, increasing supply levels of nitrogen fertilizer could improve antioxidant enzyme activity and Pn, consequently producing increased maize grain yield under waterlogged conditions.