Variations in Maize Dry Matter, Harvest Index, and Grain Yield with Plant Density

Modern maize (Zea mays L.) hybrids are generally regarded as strongly population dependent because maximum grain yields (GYs) per area are achieved primarily in high-density populations. This study was conducted to analyze changes in density independence with plant density based on the response of GY, dry matter (DM) accumulation, and the harvest index (HI) to changes in plant density. Two modern cultivars, ZhengDan958 and ZhongDan909, were planted at 12 densities ranging from 1.5 to 18 plants m(-2). The experiment was conducted for 3 yr, with drip irrigation and plastic mulching, at the 71 Group and Qitai Farms located in Xinjiang, China. With increased plant density, DM accumulation per area increased logarithmically, the HI decreased according to a cubic curve, and GY per area increased quadratically; the optimum density was 10.57 plants m(-2). Further analysis showed that the response of GY per area, DM per area, and the HI to changes in plant density could be divided into four density ranges: Range I (<= 4.7 plants m(-2)), in which DM per area, the HI, and GY per area were significantly affected by density; Range II (4.7-8.3 plants m(-2)), in which the HI was unaffected by density but DM per area and GY per area were significantly affected; Range III (8.3-10.75 plants m(-2)), in which GY per area was unaffected by density but DM per area and the HI were significantly affected; and Range IV (>= 10.7 plants m(-2)), in which DM per area was unaffected by density but the HI and GY per area were significantly affected. These results indicated that Range II is a density-independent range and Range III is a GY-stable range.