Physiological response of soybean genotypes to plant density

Response of soybean (Glycine max (L.) Merr.) to plant density has occupied a segment of agronomic research for most of the century. Genotype differences have been noted especially in response to planting date, lodging problems and water limitation. There is limited information on the physiological growth parameters (such as relative growth rate, leaf area ratio, specific leaf area ratio and shoot/root) that corresponds to different soybean genotypes response to different plant densities and how these parameters affect plant yield. The put-pose of this study was to investigate the effect of plant density on biomass production, N-2 fixation and yield of different soybean genotypes by comparing the current farmer's practice to other planting densities in the field. Further experiments in controlled climatic condition studied the physiological changes of growth parameters to different plant densities by different soybean genotypes. The result of the field experiment showed that total biomass, plant N derived from N fixation and seed yield of all three genotypes responded positively to increased plant density. Double density significantly increased seed yield per unit of area, by 93, 37 and 43% for the determinate Wuyin9, the semi-determinate You91-19 and the indeterminate Jufeng, respectively. The effect of plant density on individual plant characteristics varied in this experiment. Double density had no significant effect on individual plant biomass and seed weight per plant in the determinate genotype Wuyin9, but had a significant negative effect in the later maturing genotypes, with a reduction of 19% in biomass for both determinate Jufeng and semi-determinate You91-19. Detailed experiments under controlled climatic conditions in a growth chamber and a greenhouse in nutrient solution and soil were conducted to determine the physiological variations of growth parameters between the different soybean genotypes in response to plant density. The results showed that the negative response of the individual indeterminate Jufeng plant to planting at double density was mainly due to increases in leaf area ratio (LAR) and specific leaf area (SLA). The greenhouse experiments gave results similar to those obtained in the field. Double density had no significant effect on growth and yield of individual plants of the determinate genotype Luyuebao while it significantly decreased both biomass and yield of individual plants by 40% for semi-determinate You91-19 and 46-47% for indeterminate Jufeng, respectively. For all genotypes, yield per unit of area was higher at double than at single density. Seed yield reduction at single density was mainly associated with a decrease in pod or seed number per unit of area. (C) 2002 Elsevier Science B.V. All rights reserved.