Leaf senescence characteristics post-anthesis at different positions of spring maize canopy under different cultivation models

Post-silking is a critical period for maize yields. This study aimed to elucidate the senescence characteristics of spring maize leaves at different parts of the canopy under different cultivation modes, to understand the mechanism of yield formation and provide a theoretical basis for the regulation of senescence of maize plants in different cultivation models. Four cultivation modes with different agronomic measures were set up by integrating planting density, tillage method, and fertilizer management; they included inherent soil production (ISP), farmer household model (FP), high-yield and high-efficiency model (HH), and super-high-yield model (SH). The leaf area dynamic change model y=ae^b−cx/(1+e^b−cx) was used to analyze the senescence process of leaves, and photosynthetic pigment and antioxidant enzymes activities were measured in different parts of the leaves to compare the senescence characteristics of maize leaves under different cultivation modes. The yields of HH (12 445.55 kg∙hm⁻²) and SH (13 759.07 kg∙hm⁻²) were significantly higher than that of FP and ISP; they increased by 14.4% and 26.4%, respectively (P<0.05), compared with that of FP. The dry matter weight of SH increased by 18.5% and 10.4% compared with that of HH at silking and maturity stages (P<0.05), respectively, and that of HH increased by 2.8% (P>0.05) and 17.7% (P<0.05) compared with that of FP, respectively. Compared with FP, HH and SH started senescence later and the upper leaves were the most typical, with an average decrease in senescence rate of 26.7% and 18.0%, respectively (P<0.05). Compared with FP, the times to maximum reduction rate of relative green leaf area of HH and SH increased by 12 d and 8 d, and the maximum leaf area per plant increased by 8.7% and 6.6%, respectively (P<0.05). From 0 to 60 d after silking, the average leaf areas of lower canopy of HH and SH were 42.4% and 17.3% higher than that of FP, respectively (P<0.05). The photosynthetic pigment contents and protective enzymes activities of the lower and middle leaves of HH and SH plants were significantly higher than those of FP plants after silking. The activities of protective enzymes in the HH middle and lower leaves remained at a high level and decreased slowly during late growth period. After silking, the MDA content of all parts of the maize leaves in different cultivation modes tended to increase, and the MDA content of HH and SH remained at a lower level than that of FP. Compared with FP, for HH and SH with the integration of dense planting, deep tillage, and split fertilizer application technology, the leaf senescence started later in the upper part of the canopy during the flowering period, but the leaf area in the middle and lower parts showed higher and slower senescence. In addition, after silking, the pigment content was very high and decreased slowly, and the leaf protective enzyme activity was very high; this significantly slowed down the senescence process of middle and lower leaves and was conducive to photosynthesis assimilation and high yield.