Effects of Deep Underdrainage in the Large Scale Chinese Yam Upland Field during Growing Period in Byobusan-area, Aomori Prefecture

Abstract

The ultimate goal of this study is to clarify the relationship between the soil moisture transfer characteristics and the occurrence of tuber damages in Chinese yam in the large scale agricultural land in Byobusan-area, Aomori Prefecture developed by the government. The authors conducted volumetric water content monitoring by installing soil moisture sensors at the depth of 10, 30, 50, 100 and 150 cm of Chinese yam upland field with the deep underdrainage at Toyotomi and Shariki construction fields. Numerical simulations on soil moisture transfer in one and two-dimensional directions were also conducted in order to verify the drainage effect the deep underdrainage laid down the upland field. From the results of soil moisture monitoring in the period of thickening growth of Chinese yam, the soil water was reliably drained by internal drainage after rain and thus the soil was not in an excessive moisture condition at the depth of 50 cm, at which the growth point is expected to exist. In addition, the soil at the every depth installed the soil moisture sensors did not reach the water saturated condition throughout the growing period. Focusing on validation of the volumetric water content caused by 63 mm amount of precipitation on July 24 to 25 by using the two-dimensional numerical model, we found that the surplus soil water was reliably drained toward the deep underdrainage especially in Toyotomi construction fields which had low permeability.