抄録
Cassava is frequently damaged with a water-logging during rainy season in a sloping field of Northeast Thailand. The degree of damages depends on the topographic condition and soil profile morphology. Pie-zometers and tensiometers were installed to measure the water table levels and a tracer experiment was conducted to determine the soil water flow in a sloping field. We found the followings after analysing a three-dimensional subsurface soil water flow. After a rain water infiltrated into the soil layer and reached to the groundwater zone with the vertical flow, the watertable level came up and the groundwater flowed laterally along the down slope in the permeable sand layer. Whereas the watertable level fell rapidly at the upper points of the slope after rainfall had stopped, it lowered slowly at valley slopes where the groundwater concentrated or was retained. At that place the cassava root rot was caused with increasing watertable level less than 30 cm depth from the surface.
