Abstract
Net assimilation ratio, nitrogen contents and photosynthetic ability of rice plants were measured, using variety Norin No. 37 grown at various planting densities and dosages of fertilizer. Dry matter production in 2 weeks was compared between the community condition and isolated condition in which mutual shading was removed by cutting leaves of the adjacent hills. The results obtained were as follows : 1) The amount of produced dry matter of rice plants under the isolated condition was larger than that under the community condition during the period from 4 to 12 weeks after transplanting. It would be ascribed to that the rice plant under the community could not get sufficient light during the period. 2) Leaf area per hill had an unfavourable effect on assimilation efficiency (ΔW/ΔWAP0), as shown in figure 7, when the light intensity in the community decreased due to the increase of leaf area index. When the value of leaf area index was too high, the reduction of leaf area per hill or dense spacing of planting was considered to be beneficial for assimilation efficiency of the community. 3) Photosynthetic ability of the rice plant had an intimate correlation with the N content in leaf blades. Also the number of glumes per plant had a high correlation with the N content in the plant as well as that in the leaf blade. Accordingly, the number of glumes might indicate the photosynthetic ability of the rice plants at heading time in most cases (Fig. 9)
