玉米“正红6号”的密植效应

为发掘玉米密植增产潜力,探明耐密植玉米品种“正红6号”常规施肥下的密植效应,在川中丘陵区中江县布置田间试验,设置5.25(CK,实际生产密度)、6.00、6.75、7.50、8.25万株·hm^-2 5个种植密度,研究“正红6号”不同种植密度下生长、倒伏及产量等的响应。结果表明,随种植密度增加,株高、穗位高和叶面积指数都随之增大,而茎粗随之减小;平均每增加0.75万株·hm^-2,株高、穗位高分别平均增大6.47 cm、2.13 cm,最大叶面积指数平均增大0.46,茎粗平均减小0.46 mm。密植后,单株地上部干物质量下降,群体地上部干物质量增加;叶和茎鞘干物质转运量增加,茎鞘干物质转运率先增加后降低,而叶干物质转运率降低;成熟期各部位干物质分配比重为:籽粒>茎>叶>穗轴>叶鞘>苞叶,各部位对密植的响应不同。随着密度增加,倒伏率与倒折率显著增大,空秆率、穗下垂率增大,双穗率减小;穗数显著增加,穗长、穗粗、穗粒数、千粒质量和收获指数呈下降趋势,秃尖长呈上升趋势。籽粒产量随密度增加先增加后降低,7.50万株·hm^-2时籽粒产量最大,相比对照显著增产38.02%。由此可知,玉米密植增大了茎秆倒伏倒折风险,在一定范围内,可以通过提高群体干物质生产力来弥补单株生产力的下降,从而获得高产。经模拟,川中丘陵区“正红6号”作为春玉米的适宜密植密度为7.94万株·hm^-2。

Effect of high plant density on yield of maize variety ‘Zhenghong No. 6'

The aim of this research was to explore the potential to achieve increased yield of maize variety Zhenghong No. 6 through high plant density under normal fertilisation rates. Field trials were set up in Zhongjiang County in the central hilly region of Sichuan. Five planting densities were set up: 5.25 (CK, actual production density), 6.00, 6.75, 7.50 and 8.25×10⁴ plants·ha^-1, and the growth, lodging and yield of Zhenghong No.6 compared under the different planting densities. It was found that as planting density increased, plant height, cob length, and leaf area index all increased, while stem diameter decreased. With each stepwise increase in plant density of 750 plants·ha^-1, plant height increased on average by 6.47 cm and cob height from the ground by 2.13 cm, while the maximum leaf area index increased by 0.46, and stem diameter decreased by 0.46 mm. With greater plant density, single-plant dry weight decreased (CK, 231.5 g·plant^-1; 8.25×10⁴ plants·ha^-1, 185.1 g·plant^-1) but the crop biomass increased (CK 12153 kg·ha^-1; 8.25×10⁴ plants·ha^-1, 15271 kg·ha^-1). Across the range of tested plant densities, with increasing density, the percentage dry matter allocation to leaves and stem sheaths increased, while the allocation to stem initially increased and then decreased. Within-plant dry matter allocation was grain (~55%)>stem (~15%)>leaf (~10%)>cob>leaf sheaths>bract leaves, and proportions of each responded differently to increasing density. A calculation of % dry matter translocation at grain-fill crop development stage showed that leaf ‘translocation ratio' reduced from 18.67% to 15.04% across the tested plant density range, while stem sheath translocation ratio was greatest (20.52%) at 6.75×10⁴ plants·ha^-1. With increase in planting density, the incidence of lodging and stalk-folding increased significantly, while the incidence of empty ears, drooping ears, and double ears decreased; the ear number per ha^-1 increased significantly; ear length, ear diameter, ear grain number, 1000-kernel weight and the harvest index showed a downward trend, and bare tip length tended to increase. The grain yield was highest at 7.50×10⁴ plants·ha^-1 (10419 kg·ha^-1 and 38.02% greater than the control). Thus, it can be seen that dense planting of maize increases the risk of stalk lodging and folding, and within a certain density range, the increase in the dry matter productivity of the population more than compensates for for the decrease in productivity per plant, resulting in higher yield. Based on simulation modelling, the optimal planting density for spring maize variety Zhenghong No. 6 in the hilly region of central Sichuan under the conditions of this experiment is 7.94×10⁴ plants·ha^-1.