Abstract
Effects of different initial moisture conditions on the formation of wetted soil volume under micro-irrigation were investigated in a layered soil having a plow layer and a subsoil layer with macropores. Water was applied at a constant rate of 100 cm3 min1 for 720 minutes using a perforated tube covered with vinyl mulch. Water application efficiency was also evaluated from soil water storage and infiltration loss caused by bypass flow. In the case of initially dry condition, the wetting front was spread in an elliptical shape with the major axis in the downward direction. In the case of wet condition, however, the horizontal boundary between the plow layer having high saturated hydraulic conductivity and the subsoil layer having low one affected infiltration. Water reached to the boundary flowed horizontally and infiltrated into the plow layer from the bottom. The amount of water infiltrated vertically was more than that of horizontally infiltration in an imaginary main root zone. Infiltration loss beyond the root zone due to bypass flow was accounted for 89% in dry condition and 75% in wet condition for 720 min respectively. After 70 min irrigation, the rate of storage was unchanged in both the dry and the wet conditions. In view of water application efficiency, irrigation period exceeding about 70 minutes is inadequate.
