Abstract
The yield of the main soybean cultivars grown in Hokkaido,‘Yukihomare’, ‘Toyomizuki’, and ‘Yukishizuka’, and that of the indeterminate cultivar ‘OAC-Dorado’, which has a high yield potential in Hokkaido, were examined in experiments conducted in Ebetsu in 2023 and in Ebetsu and Obihiro in 2024. The yield obtained by twin-row cultivation (TR) (16.7 plants m−2) was compared with that obtained by conventional-row cultivation (CR). Varietal differences and the factors underlying the yield increase obtained by TR and CR were examined. In ‘Yukishizuka’ and ‘OAC-Dorado’ TR gave significantly higher seed yield (19–29%) than CR (8–27%). By contrast, the seed yield of ‘Toyomizuki’ was not increased significantly by TR. The higher seed yield of ‘OAC-Dorado’ and ‘Yukishizuka’ by TR was attributed to enhanced light interception during the reproductive growth stage, which increased the number of pods. Therefore, varietal differences in the yield-increasing effect of TR may be due to the difference in the light interception-related characteristics. For stable increase in yield by TR, specific varieties and cultivation environments need to be selected for optimizing light interception-related characteristics. Moreover, since the cultivation environment substantially influenced the improvement in light interception-related characteristics obyained by TR, implying that the cultivation environment was responsible for the unstable increase in yield among planting patterns in soybean fields.
