Abstract
The drainage effect of connecting open ditches and mole drains in upland fields converted from paddy fields, and the drainage and irrigation effects of open ditches during dry weather on soil moisture and yield of soybean were examined. Using this method irrigation during dry conditions reduced soil pF values. Therefore, soil moisture could be controlled within the effective range for reducing drought damage. In the case of rainfall of 60 mm/day or more, the minimum value of pF was higher with the installation of connecting open ditches and mole drains than without. In 2017, the effect of drainage measures ensured growth volume from the first half of the growing season. In 2018, the first half of the growing season was extremely dry, and multiple irrigations during the dry period with a pF of 2.5 or higher resulted in a higher number of nodes, whole grains, heavier one-hundred-grain weights, and higher yields compared to no installation.
