Studies on Dry Matter and Grain Production of Rice Plants : III. Analysis of dry matter productivity before heading stage

In order to analyze the causes of varietal differences in dry matter production before the heading stage, the same varieties used for the experiment, in paper II were examined. The photosynthetic rate of a single leaf (Po), the respiratory rate of each plant organ and the specific leaf area were determined. The extinction coefficient, leaf inclination and the horizontal distribution of leaves in the canopy were also determined. The results obtained are summarized as follows: 1. Varieties with a higher optimum leaf area index showed a smaller value in the decreasing rate (b) of NAR with LAI increase (Fig. 3). 2. All of the variables examined, Po, the mean leaf inclination, the variation coefficient of horizontal leaf distribution in the upper half of the canopy, and the respiratory rate, showed significant positive correlations with b (Table 3 and Table 4). On the other hand, specific leaf area showed a significant negative correlation with b (Table 3). 3. Varieties with a taller plant height and more productive tillers showed thinner leaf blades, a higher leaf area expansion speed, a low Po and lower respiratory rates (Table 4, Table 5, Fig. 5 and Fig. 6). NAR of these varieties was low at the small LAI stage of the canopy, but the decreasing rate (b) of NAR with increase of LAI in the canopy was small. Therefore, dry matter productivity at the increased LAI stage of canopy was high in these varieties (Fig. 2). 4. Varieties with taller plant height and somewhat inclined leaf blades were characterized by a uniform leaf distribution in the upper half of the canopy, so that the b value became smaller (Table 5).