2022 Volume 57 Issue 2 Pages 45-55
To improve soybean productivity, we investigated the relationships between soybean yield and growth- or field-related factors in 30 cultivated fields. First, the relationships with growth-related factors were analyzed. Under conditions of sufficient plant number, the number of branches, total number of pods per plant, and number of grains in each pod were higher and the 100-grain weight was heavier in fields with higher yield. A significant negative correlation was observed between yield and grain weight damage by stinkbugs, suggesting that timely control of these insect pests is necessary to increase the total number of pods per plant and thus increase yield. Next, with regard to field-related factors, yield was significantly correlated with ground water level, water retention time in the soil layer, and saturated hydraulic conductivity of the subsoil. To improve yield, it is therefore necessary to reduce the number of days when the groundwater level rises to less than 40 cm below the ground surface, reduce the time of water retention in the soil layer due to heavy rainfall, and to improve the physical properties of the dense subsoil. There was also a significant correlation between the number of days when the groundwater level rose to less than 40 cm below the ground surface and the water retention time of the soil layer, suggesting that the water retention time of the soil layer could be reduced by lowering the groundwater level.
