Dongpo Li

Production efficiency and effect of water management on rice yield in Japan: two-stage DEA model on 110 paddy fields of a large-scale farm

Water management is increasingly important for rice productivity to maintain soil temperature and fertility with the presence of global warming. Meanwhile, rice production in Japan is in urgent need to reduce the costs through improving the efficiency and market competitiveness. This paper aims to measure effect of water depth and water temperature on rice yield of individual paddy fields and improve the practice of water management for them. In the first stage, we measure the production efficiency of rice yield through the adoption of data envelopment analysis. The results indicate that enlarged scale of the paddy fields increases the efficiency, and rice quality can be improved more than quantity. Moreover, the most inefficiently used inputs include the amount of fertilizer nitrogen and the soil capacity, which is a compound measurement of 21 soil chemical properties. In the second stage, after comparing the 20 paddy fields with highest and lowest technical efficiency, an observation shows that the rice yield is much more affected by water temperature than by water depth. The data of all the variables used in this study were sampled in 2015 and comprised of 110 paddy fields of Koshihikari, one of the most popular Japanese rice varieties, from a large-scale farm located in Kanto Region of Japan. In the analysis, the outputs include yields of raw paddy, paddy with 15% moisture, unsorted brown rice, sorted brown rice, milled grain rice, and perfect grain rice. The inputs include the field area, air temperature, solar radiation, fertilizer nitrogen, soil capacity, and farming conditions.Graphical Abstract

Fertilizer nitrogen, soil chemical properties, and their determinacy on rice yield: Evidence from 92 paddy fields of a large-scale farm in the Kanto Region of Japan

Rice, a staple crop in Japan, is at risk of decreasing production and its yield highly depends 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 92 peat soil paddy fields on a large-scale farm located in the Kanto Region of Japan. The rice variety used was the most widely planted Koshihikari in Japan. Regression analysis indicated that fertilizer nitrogen significantly affected the yield, with a significant sustained effect to the subsequent year. Twelve soil chemical properties, including pH, cation exchange capacity, content of pyridine base elements, phosphoric acid, and silicic acid, were estimated. In addition to silicic acid, magnesia, in forms of its exchangeable content, saturation, and ratios to potassium and lime, positively affected the yield, while phosphoric acid negatively affected the yield. We assessed the soil chemical properties by soil quality index and principal component analysis. Positive effects were identified for both approaches, with the former performing better in explaining the rice yield. For soil quality index, the individual standardized soil properties and margins for improvement were indicated for each paddy field. Finally, multivariate regression on the principal components identified the most significant properties.