Abstract: The maize cultivar Zhengdan 6161 was used as the experimental material，and field experiments were conducted with four treatments spraying chemical regulator made of ethylene and cycocel with ratio of 3∶1，including CK（spraying water as control at 8‐leaf and 15‐leaf stages），T1（spraying chemical regulator at 8‐leaf stage），T2（spraying chemical regulator at 15‐leaf stage），T3（spraying chemical regulator at 8‐leaf and 15‐leaf stages），under two planting densities of 75 000 plants/ha（D1）and 90 000 plants/ha（D2）.The effects of times of spraying chemical regulator on canopy and stem characteristics of densely planted maize were studied to provide a reference for the chemical regulation technology for the reasonable canopy construction of densely planted maize populations.The results showed that the chemical regulator application reduced the leaf area index（LAI），while increased the diffuse non‐interceptance（DIFN）of population canopy.T2 and T3 treatments reached the significant levels，reduced the LAI of the ear position layer by 32.75%，24.20%（D1）and 27.61%，21.65%（D2），and increased DIFN by 46.91%，42.25%（D1）and 57.42%，47.68%（D2）respectively.Additionally，T3 treatment significantly increased the chlorophyll fluorescence parameter of PIabs（performance index on absorption basis）by 43.07%（D1）and 43.57%（D2）at silking stage，and significantly decreased plant height，ear height，and ear position coefficient under D2 condition.T1 and T3 treatments generally significantly increased the cross‐sectional area of the basal second to fifth internodes，and puncture strength of the basal third internode，and increased the cellulose，hemicellulose and lignin contents of the basal third internode by 12.39%—21.08%（D1） and 16.28%—27.58%（D2） at silking stage respectively，and there was no significant difference between the treatments of T1 and T3.Chemical regulator application could achieve yield increase by increasing the thousand‐grain weight. T2 and T3 treatments significantly increased the yield by 6.19% and 9.65% under D2 condition，respectively.D2T3 treatment had the highest yield，followed by D2T2 treatment，which increased by 25.56% and 22.57% respectively，compared to D1CK treatment. In summary，application of chemical regulator at 8‐leaf and 15‐leaf stages ultimately achieves yield increase under 90 000 plants/ha through improving the resistance to lodging by reducing the plant height，ear height and ear position coefficient，increasing the cross‐sectional area of the basal internodes and puncture strength of the basal third internode，improving the contents of cellulose，hemicellulose and lignin in the cell walls of stems，and optimizing the canopy structure and leaf fluorescence parameters，which is the optimal measure for yield increase in this region.

Key words: Maize, Time of spraying chemical regulator, Dense planting, Canopy characteristics, Stem characteristics

摘要： 以玉米品种郑单6161为试验材料，设置2个密度（D1：75 000株/hm²；D1：90 000株/hm²）、4个化控剂（化控剂为乙烯利和矮壮素3∶1）喷施时期（CK：8展叶期和15展叶期均喷施清水；T1：8展叶期喷施化控剂；T2：15展叶期喷施化控剂；T3：8展叶期和15展叶期均喷施化控剂），研究化控时期对密植玉米群体冠层和茎秆特性的影响，为密植玉米群体提供合理的化控时期。结果表明，与CK相比，3个化控处理均可以降低密植玉米群体叶面积指数（LAI），提高无截获散射（DIFN），T2、T3处理达到显著水平，分别使穗位层LAI 降低32.75%、24.20%（D1）和27.61%、21.65%（D2），使DIFN 提高46.91%、42.25%（D1）和57.42%、47.68%（D2）。此外，T3处理吐丝期叶片叶绿素荧光参数光合性能指数（PIabs）分别提高43.07%（D1）和43.57%（D2），株高、穗位高及D2下穗位系数均显著降低。T1和T3处理总体上显著增加基部第2—5节间横截面积、基部第3节间穿刺强度，使吐丝期基部第3节间纤维素、半纤维素、木质素含量分别增加12.39%~21.08%（D1）和16.28%~27.58%（D2），2个处理间差异均不显著。化控处理通过提高千粒质量实现增产，T2和T3处理使D2下产量显著增加6.19%和9.65%。产量以D2T3处理最高，D2T2处理次之，分别较D1CK处理增产26.56%和22.57%。综上，在90 000株/hm2条件下，8展叶期和15展叶期均喷施化控剂可以通过降低株高、穗位高、穗位系数，增加基部节间横截面积和基部第3节间穿刺强度，提高茎秆细胞壁纤维素、半纤维素和木质素含量，来提高群体抗倒伏能力；通过优化冠层结构和叶片荧光参数，最终实现密植增产，为该地区实现增产的最佳措施。

关键词: 玉米, 化控时期, 密植, 冠层特性, 茎秆特性