Effects of Different Controlled Nitrogen Ratios on Leaf Senescence and Grain Filling Characteristics of Summer Maize

Supplying nitrogen timely and effectively could delay leaf senescence and improve grain filling characteristics of maize. The effects of controlled-release fertilizers with different controlled nitrogen ratio on leaf senescence, grain filling and yield of summer maize were studied to explore the appropriate controlled nitrogen ratio for summer maize in Huang-Huai-Hai region.

This study was conducted in 2019-2021 cropping seasons, using the middle-early maturing hybrid Denghai 518 (DH518) and the middle-late maturing hybrid Denghai 605 (DH605) as experimental materials. The types of nitrogen fertilizer are controlled release urea and ordinary urea mixed, ordinary urea. Five controlled nitrogen ratios: 10% (T1), 20% (T2), 30% (T3), 40% (T4) and 50% (T5) were set for studying the effects of controlled-release fertilizers on leaf senescence, grain filling characteristics, and their inter-relationship of summer maize, using urea fertilizer treatment as control (CK).

The results showed that using controlled release fertilizers could significantly increase the yield of summer maize. Among these, the yield increased most significantly in T3 treatment. Compared with CK, using controlled release fertilizers significantly increased the leaf area index (LAI), SPAD value, and the antioxidant enzymes activities, thus improving the grain filling characteristics. Among these, T3 treatment increased the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in summer maize leaves at the late growth stage, reducing the accumulation of malondialdehyde (MDA), thus delaying leaf senescence most significantly. In addition, the maximum growth (W_max), grain filling rate (G_max), days of active filling period (P), and grain dehydration rate were increased mostly in T3 treatment, accordingly the 1000-kernel weight and grain yield of summer maize were increased mostly. Correlation analysis showed that the yield was positively correlated with W_max and G_max; W_max and G_max was positively correlated with the activities of SOD and POD, but negatively correlated with MDA content. Grain dehydration rate and grain filling rate were positively correlated with the activities of SOD and CAT, but negatively correlated with MDA content. The water content of kernels was negatively correlated with the activities of SOD and CAT, and positively correlated with MDA content. Therefore, using controlled release fertilizers, especially T3 treatment, effectively optimized the grain filling characteristics by increasing the antioxidant enzyme activities, thus increasing the grain yield of summer maize.

Using controlled-release fertilizer could effectively increase the activities of leaf antioxidant enzymes, thus delaying leaf senescence, improving grain filling characteristics and increasing grain yield of summer maize. Among these, T3 treatment increased the grain yield most significantly.