Soil infiltration and runoff path on afforestation of plain areas at Pingtung of southern Taiwan

Soil infiltration was one of important factors in affecting soil and water losses. If soil infiltration on hillslope was large, the rainfall excess would be small. Then surface runoff and soil loss of slopeland would be also small. This study used pond-type infiltrometer to perform measuring infiltration rates on forest plantation and neighboring orchard and grass lands at Shihlin and Linhou farming land of Chaochou area, Pingtung County of southern Taiwan. The final infiltration rates of topsoil at different land uses were as follows: forest plantation (103.7 mm/h), grass land (56.1 mm/h), and orchard (42.0 mm/h). The final infiltration rates of subsoil at different land uses were as follows:forest plantation (9.9 mm/h), grass land (13.3 mm/h), and orchard (6.9 mm/h). Final soil infiltration rates were decreasing from topsoil to subsoil. The final infiltration rate of topsoil at forest plantation was smaller than rainfall intensity (103.8 mm/h) of 50 recurrence years at Pingtung, so no Horton's overland flow happened to forest plantation every 50 recurrence years. However, the final infiltration rate of subsoil at forest plantation was smaller than rainfall intensity (53.2 mm/h) of 1 recurrence year at Pingtung, so saturation overland flow happened to forest plantation every recurrence year. The final infiltration rate of topsoil at grass land was smaller than rainfall intesity (62.2 mm/h) of 2 recurrence years at Pingtung, so Horton's overland flow happened to grass land every 2 recurrence years. The final infiltration rate of topsoil at orchard land was smaller rainfall intensity of 1 recurrence year at Pingtung, so Horton's overland flow happened to orchard land every recurrence year. The final infiltration rates of subsoil at orchard and grass lands were smaller than rainfall intensity of 1 recurrence year at Pingtung, so saturation overland flow happened to orchard and grass lands every year.