Abstract
The productive structure and the light distribution characteristics at early ripening stage in mixed-sowing community of rice were examined at two fertilizer levels on well drained paddy field. And the relationships between their results and lodging resistance, or and matter production were discussed. Two cultivars 'Koshihikari', tall and lodging-susceptible, and 'Kanto No. 100', short-statured and lodging-resistant, were used. Both of them are of the same maturity. Koshihikari and Kanto No. 100 were sowed alternately to two rows and two rows, or one and one, respectively. 1. The effects to mixed sowing on productive structure under one row alternate mixture were more remarkable than those under two rows alternate mixture. The fresh weight of assimilatory and nonassimilatory organ increased by mixtures in the upper layer of structure in Koshihikari and decreased in the middle-low layer in Kanto No. 100. Consequently more increase of the rate of upper layer weight was recognized in the mixed stands involved two varieties, compared with the mean value of the pure stands of the two cultivars. 2. The light receiving structure of Koshihikari obviouly was made better on all layers in mixtures and that of Kanto No. 100 was made worse except on lower layer. However, the light receiving structure of mixed stands involved two varieties was clearly better than that of pure stands of Koshihikari, but not beyond Kanto No. 100, and it was superior to the mean structure of the pure stands of the two cultivars. These suggest that 'the active effect of cooperation' was appeared in the light receiving structure. Those results were confirmed by usual comparison methods of the productive structures and the extinction coefficient K. Furthermore, the vertical light receiving distribution was able to be compared relatively and quantitatively to some degree by using light receiving index (relative illuminance ×leaf area index of each stratum) proposed in this report. 3. It was considered that the intensification in lodging resistance (such as the increase of the breaking strength) of Koshihikari by mixed sowing was closely related to the improvement of the light receiving structure at the early ripening stage through the maintenance of activities in the leaves and leaf sheathes occurring at the lower nodes. 4. The crop growth rate (CGR) and the net assimilation rate (NAR) during ten days after the investigation of the production structure were correspondent with the quality of the light receiving structure. The CGR and the NAR of Koshihikari increased in mixtures and those of Kanto No. 100 decreased, however, those of mixed stands involved two varieties were larger than the mean value of the pure stands of the two cultivars. In those growth parameters the active effects of cooperation were also recognized. 5. The artificial condition of no lodging was set up through stretching a net. In the top dry weight the active effects of cooperation were recognized correspondingly with those in the light receiving structure, but those effects were not recognized in the yield. Therefore, it seemed to be difficult to gain the active effects of cooperation for the yield by mixed sowing without the secondary effects such as the prevention of lodging that the improvement of the light receiving structure accompany.
