Variation of soybean yield among regions and years in Tohoku district and its relation to meteorological factors

Abstract

We investigated the variation in soybean yield with the year and region in the Tohoku district for 16 years from 1993 to 2008, and analyzed the relationship between the yield variation and meteorological factors in each region. For analysis, we employed five meteorological factors: precipitation, daily mean temperature, daily maximum temperature, daily minimum temperature and the duration of sunshine. We selected 41 municipalities where soybean acreage exceeded 100 ha per municipality. Investigation of yearly variation of soybean average yield in each prefecture revealed that the yield level was higher in prefectures facing the Sea of Japan than in those facing the Pacific Ocean, and that it was higher in southern regions in the former prefectures but in the northern regions in the latter prefectures. Yearly variation of the average yield per prefecture was positively correlated in Aomori, Iwate, Akita and Yamagata prefectures, while that in Miyagi and Fukushima was correlated only with the adjacent northern and southern prefectures. Analysis of the relationship between yearly yield variation and meteorological factors in individual municipalities indicated that meteorological factors in July significantly correlated with the yields in many cases, and that the relative contribution of the major meteorological factors (precipitation, temperature and the duration of sunshine) to the yield variation varied with the municipality.