Soybean and Winter Wheat Production by Subirrigation Using Underdrain Cleaning System in Paddy Fields

Abstract

We investigated a method for utilizing the underdrain cleaning system in paddy fields in Hokkaido as a means of subirrigation for soybean and winter wheat. During the period of greatest soil water uptake by these crops, the set water level was 30 cm below the surface when the soil water potential of the primary root zone fell below -31 kPa, and subirrigation was carried out by using the underdrain system one day after reaching the set water level. The results demonstrated that both growth and grain yield were increased by subirrigation. In addition, we calculated the number of days until the soil water potential in the root zone returned to -31 kPa or less after rainfall or subirrigation using the observation data for soil water potential. Based on these results, we proposed a method by which subirrigation is conducted more than 10 days after 20 mm or more of event-wise precipitation for soybean fields and more than 15 days after 20 mm or more of event-wise precipitation for winter wheat fields.