Assessment of soybean productivity and its changing factors in Japan based on the production cost statistics

Soybean (Glycine max [L.] Merr.) yields have remained below 2.0 t ha^-1 for over 30 years in Asian countries, indicating long-term stagnation in productivity and production technology. This study aimed to measure the total factor productivity (TFP) of soybean production in Japan and to assess the factors affecting TFP and yield. The Färe-Primont index of TFP was measured for two agroclimatic regions using soybean production cost statistics from 1987 to 2015 to analyze the regression of TFP and yield with per-farm land size, time trends, and production-related input variables. The TFP increased by 1.5-2.4 % annually in the two regions, despite an annual decrease of 0.7 % in country's average yield. The TFP in the subarctic Hokkaido region improved by 9-15 % due to the land-size increase and progress of time, i.e., technological progress, during the period. While in the temperate main-island region, a 14 % TFP increase induced by increased land size was largely offset by the time-progress effect (-11 %), i.e., technological retrogression. Similar time-progress effects observed on yield indicated that technological changes occurred, with respect to cultivation methods. The TFP-improving land-size increase adversely resulted in a 9 % yield decrease in the main-island region accounting for 85 % of soybean cultivation area in Japan. The results further showed that TFP improved by saving production inputs, such as fertilizer, per unit area in both regions, and the yield rose with increased inputs in seed, agrochemicals, and rental services, depending on the region. This study revealed continual soybean TFP improvements across Japan due to land-size increases and input saving in addition to the regionally biased progress in cultivation technologies. The implications of the results are discussed from the perspective of improving TFP and yield while increasing the per-farm land size.