2023 Volume 92 Issue 2 Pages 161-172
Recently, the yield of soybean in Fukuoka and Saga Prefecture, which are the major soybean producers in northern Kyushu, is decreasing, while rainfall during the growth period is increasing. Soybean yield was significantly and negatively correlated with rainfall during the growth period, which indicates that wet injury negatively affects soybean yield. This study aimed to clarify the effect of a new planting method involving one-step shallow tillage planting using an up-cut rotary in preventing the reduction of soybean yield caused by wet injury in a field in northern Kyushu. Field studies were conducted from 2019 to 2021. Heavy rainfall occurred just after planting in 2019 (mid- to late July), at the early reproductive stage (mid-September) in 2020, and vegetative stage (early to mid-August) in 2021. In 2019, due to defective germination caused by wet injury, the farmer had to re-plant the seedlings after conventional planting (control) , while good seedling establishment was obtained using the new planting method. The yield was 36% lower in the control than when the new planting method was used, due to delay in plant growth caused by later planting in the control. In 2020 and 2021, the duration of over-humidity in soil was approximately twice longer and the yield was 26 and 40%, respectively, lower in the control. On a 3-yr average, the new planting method prevented the reduction of yield caused by wet injury by 34%.
