Abstract
Rice plants, cv. Koshihikari were grown on a fine-textured gley paddy soil at Fukui Pref. Agric. Exp. Stn.. Plants were grown under full (control plot) and 78% of full solar radiation (shaded plot) with shade cloth from panicle formation stage till heading. Effects of shading on root length density (RLD), root length, root distribution and grain yield of rice plants were determined. Samples taken both in and between hills, at the 0-20 cm soil depth, showed that RLD was lower in shaded plot than in control plot. There was no significant difference in RLD between shaded and control plots at the 20-30 cm soil depth. The total root length per 10 a (30 cm depth) was estimated with RLD. The total root length of shaded plot (38, 100 km/10 a) was 20% less than the control (49, 200 km/10a). The grain yield in shaded plot was approximately 10% lower than the control. The main effect seemed to be a decrease in the number of grains per head, however, there was also a decrease in percentage of ripened grains and grain weight. These results indicate that solar radiation during panicle formation to heading affects root system morphology and grain yield of rice plants. Also there are strong relationships between both mass and distribution of roots and grain yield of rice plants.
