Water dynamics during the drying process in poorly tilled plow layer of clayey paddy field adversely affecting soybean germination

Abstract

In Japan, most soybeans are cultivated in paddy fields, but its yields remain low. The causes are thought to be wet damage due to low drainage efficiency, dry damage due to summer drought, and reduced available nitrogen, which have been the focus of intensive research. However, less attention has been paid to poor soil tilth, which is particularly pronounced in clayey paddy field. In such poorly tilled plow layer, greater soil moisture depletion occurs, potentially leading to reduced germination rate of soybean seeds. This paper reviewed existing research on soil friability in the clayey paddy field, optimal clod size for germination of soybean seed, characteristic unsaturated liquid and water vapor movement in the soil layer composed of clods, and resulting soil desiccation. It also introduced farming techniques to overcome the poor soil tilth. Based on these reviews, future research topics were proposed.