In this text the layer-cutting method in crop field (M. Monsi and T. Saeki, 1953) is adopted. The produce structure of communities, the distribution of light and the variation of extinction coefficient within communities under different density condition of the millet are studied. The aim is to findout a rational density of millet and a simple method for determinating daily average extinction coefficient.
The experiment results are shown as follows:
1．Aerial biomass, ear weight and LAI etc. of the community of medium density are 724.5g/m2, 289.81g/m2, 2.95 respectively, they are the highest in the communities with different density. It is shown the density between 45000--50000/mu are suitable.
2. It assumes positive correlation between density of community and extinction coefficient. The extinction coefficient increases with density. It shows negative correlation, between the extinction coefficient of communities and the average value of light intensity within communities.
3. The tendency of diurnal variation of extinction coefficient of different millet communities is presented as a depression shape curve i. c. higher at the morning and evening, lower at noon. Through practical measure, we can see that the instantaneous k value at 9. a. m. or 3. P. m. approximates to diurnal average value of the community during the day. Thus each of them instantaneous k value may be considered as approximate value of daily average k value.