Abstract
Rice yield was estimated from that in 30 hills harvested at the center of each paddy field in Kikuchi district Kumamoto Prefecture in 1985. The rice fields surveyed were managed by two groups of innovative farmers who aimed to improve the stagnant grain yield of 5t/ha. Grain yields at 50 spots in 43 paddy fields varied from 7.44t/ha to 5.54 t/ha and the difference was not related to planting density, number of panicles per unit land area, grain-straw ratio, and 1000 grain weight, but related to grain yield per panicle. The grain yield level was associated with the maximum number of stems per unit area and the percentage of fruit bearing stems. The relations among yield level, the maximum number of stems per unit area and the percentage of fruitful stems were denoted as follows:580 panicles/m2→80%→6.6t/ha, 580 panicles/m2→70%→6.3t/ha, 480 panicles/m2→80%→5.7t/ha. The relationship between the increased stem number from 16 to 23 July and grain yield irrespective of soil texture, the kinds of winter crops, and fertilizer. The relations were denoted as follows : 230 panicles/m2→6.6t/ha, 200 panicles/m2→6.3t/ha, 160 panicles/m2→5.4t/ha.
