Two–Stage DEA on Technical Efficiency and the Effect of Water Management on Rice Production of 122 Paddy Fields from a Large–Scale Farm in Japan

In Japan, rice production is undergoing a transition from acreage reduction to an improvement in efficiency and competitiveness. Owing to the global warming, water management is increasingly important in maintaining soil temperature and fertility for rice productivity. This paper aimed to measure the production efficiency of rice yield, using a two–stage data envelopment analysis (DEA). The data comprised of 122 paddy fields of Koshihikari, one of the most popular Japanese rice varieties, which were sampled from a large–scale farm located in the Hokuriku Region of Japan in 2015. In the first stage of the analysis, the outputs included yields of raw paddies, paddies with 15% moisture, unsorted, sorted, perfectly shaped, and milled brown rice. The inputs included the field area, temperature, solar radiation, fertilizer nitrogen, soil capacity, and farming conditions. The results indicated that there was a large margin to increase the yields, and an enlarged scale could increase the efficiency of most paddy fields; the largest input slacks occurred in land capacity and field area. In the second stage, we determined the significant effects of water management on rice production efficiency at different growth stages in the 20 paddy fields of highest and lowest efficiency. Finally, we discussed the interactions between air temperature, water depth and water temperature.