关键词: 玉米, 化控时期, 密植, 冠层特性, 茎秆特性

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