Modeling of phenological development stages and impact of elevated air temperature on the phenological development of soybean cultivars in Japan

This study aimed to estimate the large-scale effects of elevated air temperature on the phenological development of soybean by using the agro-meteorological grid data. A logistic model has been developed for describing the developmental rate (DVR) of three soybean cultivars, Ryuhou, Enrei and Fukuyutaka. Root mean square errors of the model estimation ranged from 1.4 to 2.2 days for emergence (VE) to flowering (R2) and 1.2 to 2.8 days for R2 to beginning of seed growth (R5). The model could estimate the effect of elevated air temperature on phenological development in a temperature gradient chamber. The response of DVR to air temperature change from VE to R2 was larger in the medium cultivar, Ryuhou, Enrei, than in the late cultivar, Fukuyutaka. The elevated air temperature simulation (+3°C) resulted in shortened duration of VE to R2 in the cool, early sowing region of eastern Japan by 5 to 7 days, whereas little effect was observed in the warm, late sowing region of Kyushu, in southern Japan. This large influence of elevated air temperature on the phenological development of soybean in eastern Japan was not only because of the use of cultivars sensitive to air temperature change but also because of the range of regional air temperatures, which largely alters the DVR during the cultivation period.