Effects of early planting and cultivars on the yield and agronomic traits of soybeans grown in southwestern Japan

Abstract

Early planting contributed to increased soybean yields in the U.S. Because a double-cropping system dominates in southwestern Japan, early planting is not performed; it is thus unclear how much the yield potential could be increased by early planting. To address this question, we planted seven U.S. and five Japanese cultivars on around 20 May (early planting), measured the agronomic traits, including yield, yield components, and oil and protein contents, and compared these traits with those of the same cultivars planted on around 20 July (normal planting). In the early planting, the yields of the U.S. cultivars were 322–453 g m−2, whereas the highest yield among the Japanese cultivars was only 315 g m−2, which is significantly lower than those of the top five U.S. cultivars, indicating the adaptability of U.S. cultivars to early planting. The increases in yield obtained with early planting were 99–199 g m−2 and −26–144 g m−2 for the U.S. and Japanese cultivars, respectively. The yield obtained by early planting was positively correlated with the pods m−2, seeds pod−1, and oil contents, but negatively correlated with the sterile pod rate, 100 seed weight and protein content. In the early planting, the U.S. cultivars had greater pods m−2, seeds pod−1 and oil content and less sterile pod rate, 100-seed weight, and protein content than the Japanese cultivars. These results suggest that early planting can increase the yield in southwestern Japan, if cultivars with agronomic traits observed in the U.S. cultivars of this study are grown.

Keywords

• Adaptation
• cultivar difference
• early planting
• soybean
• yield potential