Relationships of particle size distribution curve, soil water retention curve and unsaturated hydraulic conductivity and their implications on water balance of forested and agricultural hillslopes

The primary objectives of this study were to determine selected soil water retention curves for Finnish forest sites and to develop a methodology that predicts the water retention curve and unsaturated hydraulic conductivity from the particle size distribution curve. The method was obtained by modifying Andersson's method. Selected soil water retention curves were determined for four Finnish forest site types. Parameters of 360 soil samples were estimated. The samples were collected from 90 forest soil profiles. In each profile four podzol horizons were selected for sampling. The parameters are usable for water balance calculations of various scales. The study includes results of numerous water retention characteristics and hydraulic conductivity predictions from the particle size distribution curve. These predictions were accomplished for both forested and agricultural soils. Predicting water retention characteristics from particle size distribution curve could be accomplished at a reasonable level of accuracy when the semi-physical and van Genuchten's methods were used. Predicting the water retention characteristics using Jonasson's method was successful when clay content of soil was less than 25 percent. Implications of soil hydraulic properties on water balance of forested and agricultural hillslopes showed reasonable agreement with the measured values. The best overall fit between measured and calculated values was obtained in the case that water retention curve was estimated from particle size distribution curve and unsaturated hydraulic conductivity using Andersson's method.reviewe