Impact of soil chemical properties on rice yield in 116 paddy fields sampled from a large-scale farm in Kinki Region, Japan

Japan is in urgent need to reduce the production costs through increasing rice yield, which depends highly on soil fertility. This study aimed to investigate determinants of rice yield, from the perspectives of fertilizer nitrogen and soil chemical properties. The data were sampled in 2014 and 2015, from 116 paddy fields, on a large-scale farm located in the Kinki Region of Japan. The rice included Koshihikari and other seven varieties, cultivated in conventional, special and organic regimes. The nine soil chemical properties included pH, 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 identified for silicic acid, exchangeable potassium, and ammonium nitrogen; while phosphoric acid affects the yield negatively, controlling the rice variety, cultivation regime, and field area. Finally, countermeasures were put forward to improve soil fertility and rice yield.