Hayashi's theory of quantification No.1 was used to examine the controlling factors of the paddy-rice yield in the Usa plain, Oita prefecture. The rice yield of the years 1984, 1985 and 1986 was employed as a criterion variable, and the following independent variables as items: year, soil type (soil series group), rate of nitrogen fertilizer application, soil reaction of a plow layer, and cation-holding capacity of a subsurface layer. The multiple correlation coefficient was 0.78, so 61% of the total variance in the yield was explained. Year gave the highest partial correlation coefficient (r=0.70), followed by soil type (r=0.56). The item year is an indication of weather in the rice cultivation season of that year. Thus, the weather of the rice cultivation season is the most important item to control the paddy-rice yield. The items such as rate of nitrogen fertilizer application, soil reaction of a plow layer, and cation-holding capacity of a subsurface layer hardly contributed to the size of the rice yield. These items are relating to management practices, so the soil management should be practiced depending on weather and soil type.
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