Impact of Soil Fertility in 116 Paddy Fields of Kinki Region

Japan is in urgent need of reducing its rice production costs through increasing yield, which is highly dependent on soil fertility. This chapter investigated the determinants of rice yield, from the perspective of nitrogen fertilizer and soil chemical properties. The data were collected in 2014 and 2015, from 116 paddy fields, on a large-scale farm located in the Kinki Region. The rice included Koshihikari and other seven varieties, cultivated using conventional, special, and organic methods. The nine soil chemical properties were: pH value, cation exchange capacity, ammonium nitrogen, effective phosphoric and silicic acid, saturation of base elements, exchangeable potassium, lime, and magnesia. Multiple regression analysis indicated that positive effects were found for silicic acid, exchangeable potassium, and ammonium nitrogen; while phosphoric acid affects yield negatively, while controlling rice variety, cultivation regime, and field area. Finally, countermeasures are put forward to improve soil fertility and rice yield.