Abstract
The growth pattern and productive system of napier grass (Pennisetum purpureum SCHUMACH.) and corn (Zea mays L.) plants grown in field were comparatively studied to find the principal factors determining the high productivity of napier grass. 1. At the early growth stage (planting to June) of napier grass, the number of stems highly increased to about 100 stems/m^2 for 23 days after planting, and the leaves and stems elongated horizontally covering the ground. By which the structure of plant population was improved to have a higher light utilization efficiency at the growth stage with relatively low leaf area index (LAI). 2. In summer, the middle growth stage (July to August) of napier grass, the number of stems of napier grass were rapidly decreased by self-thinning to about 25 stems/m^2. However, due to a high rate of leaf expanding at high temperature, the plant population came to have a large leaf area index (LAI=13.3). In addition, the stem elongated rapidly and its elongating angle turned from horizontal to vertical direction. These phenomena caused the improvement of productive structure in napier grass, and the light extinction coefficient (K) in the plant population reduced to K=0.4. Therefore napier grass could preserved a high net assimilation rate (NAR) in this season, and the maximum crop growth rate (CGR) reached 53.3 g/m^2/day , while NAR of corn plants did not increase in this season because the population structure was not improved so much. 3. Even at the late gowth stage (September to November), napier grass hold a relatively high LAI because the plants could compensate for the leaf area reduction with scenescence by the continuous emergency of new leaves. 4. Napier grass changed the population structure adequetely according to the growth environment to create a high efficiency of light utilization and high productivity through the whole growth stages. The final dry matter weight of napier grass was 4.4 kg/m^2, two-fold that of corn plants.
