Optimal rate of nitrogen fertilizer improves maize grain yield by delaying the senescence of ear leaves and thereby altering their nitrogen remobilization

Abstract

ContextNitrogen fertilization affects maize grain yield through regulating ear leaf senescence and nitrogen remobilization (RemN), yet few studies focus on how nitrogen alters the onset of leaf senescence and then affects leaf RemN to regulate grain-filling. ObjectiveThis study aimed to investigate the relationship between the onset of ear leaf senescence, ear leaf RemN, and grain-filling. MethodsA field experiment in Yancheng, China,with six nitrogen rates (0, 67.5, 136.5, 205.5, 274.5, and 343.5 kg N ha−1) were conducted and ear leaf senescence and grain-filling were analyzed in response to different N fertilizations. ResultsOptimal nitrogen fertilization (around 205.5 kg N ha−1) significantly increased grain yield (average 10359.2 kg ha−1) and harvest index (HI, average 0.58). Additionally, nitrogen application increased the nitrogen concentration of ear leaves and delayed senescence. The maximum delay was 3.4 days compared to the control. At the time of maximum grain yield, the onset of senescence could be delayed by 1.6–1.9 days. However, delayed senescence of ear leaves negatively impacted leaf RemN contribution to grain nitrogen, with a maximum limit of 16.0 observed at 205.5 kg N ha−1. Furthermore, nitrogen fertilization could reduce the maximum grain-filling rate (Gmax), the maximum grain weight (Wmax), and the time to reach the maximum grain-filling rate (Tmax). Higher grain yield and its response to nitrogen relied on a shorter time interval between the onset of senescence and Tmax. At a nitrogen fertilization rate of 196.85 kg N ha−1 (close to the optimal rate of 205.5 kg N ha−1), the minimum time interval could be reduced to about 2.4 days, resulting in a maximum relative yield response to nitrogen of 39.98%. Conclusion and implicationOptimal nitrogen fertilization improved grain yield by delaying the onset of senescence of ear leaves and altering its RemN, thus impacting grain filling. It provided valuable insights for achieving higher yields under the optimal nitrogen fertilization by considering the onset of ear leaf senescence, the ability of RemN in relation to grain filling.