[Effects of planting date and density on population physiological indices of summer corn (Zea mays L.) in central Shaanxi irrigation area].

By using D-saturation optimum design and the methods of crop population physiology, this paper studied the effects of planting date and density on the population physiological indices of summer maize Shandan 8806 and its yield in central Shaanxi irrigation area. The results showed that in the period from 13 June to 22 July, the delay of planting had negative effects on grain yield, dry matter accumulation (DMA), maximum leaf area index (LAImax), net assimilation rate (NAR), leaf area duration (LAD) and crop growth rate (CGR), with larger effects on LAD and CGR than on LAImax and NAR. Within the range of 45 000-65 918 plants . hm (-2), planting density had positive effects on grain yield, DMA, LAImax, LAD and CGR but negative effect on NAR, with larger effects on LAImax, LAD and CGR than on NAR. The effects of planting date were more significant than those of planting density, and thus, Shandan 8806 should be sowed as early as possible. The regressive model based on the population physiological indices indicated that for the high yield of summer maize Shandan 8806, the optimum planting date was from 10 to 20 June, and the optimum planting density was from 57 767 to 71 706 plants . hm(-2).