Abstract:

To provide further evidence for the regulatory effect of plant densities on the important characteristics of leaf area index (LAI), the important feature of the regulation role for the parameters, such as the velocity of LAI change, mean LAI, the maximum LAI and the time to maximum LAI was analyzed quantitatively. A field experiment using two spring-maize cultivars, Jidan 209 and Zhengdan 958, was conducted with five different densities from 4.5×10⁴ to 10.5×10⁴ plants ha^-1 in 2005 and seven different densities from 3×10⁴ to 12×10⁴ plants ha^-1 in 2006 in Jilin province, respectively. An extensively suitable LAIsimulation model for high yield population, y= (a+bx)/(1+cx+dx²) was adopted in the present research to simulate and analyze the effect of different densities on the dynamic characteristics of LAI in development of spring-maize in whole growth duration. The results indicated that maximum LAI was significantly increased with the increase of planting density from 3×10⁴ to 12×10⁴ plants ha^-1 and the time to the maximum LAI advanced with increasing plant densities. The relative LAI of different densities showed large difference between before and after reaching the maximum LAI. LAI of high density decreased more rapidly than that of low density. The mean LAI in whole growth duration increased while the ratio of mean LAI to the maximum LAI declined with increasing densities. The influence of density on each parameter of model equation by applying the relative model was different, that between intervals of 3×10⁴ plants ha^-1 was significant. The trend of changes on different parameters was different. The parameter a approached to 0, therefore, density has little effect on it. The parameters b and c reduced with increasing densities, but d increased with increasing densities. The velocity of LAI change in growing period showed the trend of a curve of N shape with variable speed, and the changed trend of LAI fit into growth at ages. The velocity of LAI change in high-density population increased or decreased larger than that in low-density population. The jointing period and the big flare periods were in response to density sensitively. The results above proved that some important indexes are more sensitive to different densities, such as the changing velocity of group LAI, the maximum LAI, the time to the maximum LAI, mean LAI, and the ratio of mean LAI to the maximum LAI. These characteristic indexes of LAI may serve as the reference for regulating plant density of spring maize population.

Key words: Spring-maize, Density, Leaf area index(LAI), Mean leaf area index(MLAI), Velocity of LAI change