抄録
The experiment was performed to find out the effect of irregular disposition of drill-seeded rice plants upon yield in direct sowing culture. Row of 1 m length was divided into ten equal sections (10 cm row) and number of plants in them was varied. Co-efficient of variation (cv) of number of plants in 10 cm row was used as the index of irregular disposition and five plots of cv 0 %, 30 %, 60 %, 100 %, and 150 %, were established. 1. The more irregular disposition of plants was, the more decrease in grain weight (per unit area) was. It's degree was more remarkable in Fujiminori (early maturing and panicle type variety) than in Manryo (medium maturing and medium tiller type variety). 2. Decrease of grain weight was caused by that of number of panicles (per unit area). In Fujiminori, number of panicles decreased according as irregularity in disposition of plants increased. grain weight per panicle being remained unchanged. Therefore grain weight decreased in proportion to increase in irregularity of plant disposition. In Manryo, however, grain weight per panicle increased though number of panicles decreased. Accordingly decrease of grain weight compared with the plot of cv 0 % was not observed in plots of cv 30∼100 %. 3. In Fujiminori, decrease of grain weight with irregular disposition of plants was more marked in the case of low seeding density than in that of high one. In Manryo, however, the difference of the effect of irregular disposition on grain weight caused by different spacing densities was not clear.
