Hydraulic researches of irrigation water in rice-fields, in Japan : II. On the form of rice-fields and the transition of pressure gradient in soil during the irrigation period

Hydraulic gradients in soil of the rice-fields are characterised by the form of the levee (a low dike separating one rice-field from another). Then, the fieldtype can be classified as follows : A Type......rice-field with a levee between the horizontal adjacent fields. B Type......rice-field with a levee between the undulating adjacent f ields. C Type,.....rice-field with a levee facing to lower canal or road. In Japan, a greater part of rice fields on alluvium belongs to A Type, that the pressure gradient at J_0-20, J_10-20 is so small except permeable soil structure, and the percolation is restrained ? in the rice-fields filled with water. Therefore, the pressure gradient in soil should ? be considered as an important factor concerned with seepage loss of irrigation water.湛水状態下における水田土壌水圧状態, 並びに水稻栽培期間―――灌慨期間を通して, これらの変動の特性と, 水田形態, 土壌構造の関係について述べる