Optimizing Pedotransfer Functions for Predicting Soil Moisture of Wetting Curve Based on the Effective Degree of Saturation

Abstract

Hysteresis of soil water retention curve (SWRC hysteresis) is widely used for modeling water flux in an unsaturated soil during infiltration and irrigation processes. The aim of the work was to predict soil moisture of a wetting curve from the main drying branch based on an effective degree of saturation for the drying branch by suggesting pedotransfer functions (PTFs). Furthermore, the efficiency of the proposed PTFs (M-1) was estimated by comparing it with a model having the same purpose such as a model of Mualem (1977) (M-77). The drying and wetting branches were measured using capillary meter at soil water pressure heads lower than –1000 mbar. The effective degree of saturation for drying $$S_{d}^{e}\left( h \right)$$ and wetting $$~S_{w}^{e}\left( h \right)$$ curves was estimated at different values of soil water pressure heads. The proposed PTFs (M-1) $$S_{w}^{e}\left( h \right)~$$ = $$\frac{{\sqrt 3 }}{2}$$ $$S_{d}^{e}\left( h \right)$$ was derived by dividing the mean values of $$S_{w}^{e}\left( h \right)$$ to the mean values of $$S_{d}^{e}\left( h \right)$$ . The results show that the estimation error for the proposed PTFs (M-1) and the Mualem model (M-77) was less for estimating soil moisture of a wetting curve at the higher values of soil water pressure heads as –500, –700 and –900 mbar than their values calculated at the lower values of soil water pressure heads as –50, –150, and –300 mbar and near of saturation. While the proposed PTFs (M-1) was more accurate than the Mualem model (M-77) for calculating soil moisture of a wetting branch at a saturation point and at the lower values of soil water pressure heads as –50, –150, and –300 mbar. The proposed PTFs (M-1) $$S_{w}^{e}\left( h \right)~$$ = $$\frac{{\sqrt 3 }}{2}$$ $$S_{d}^{e}\left( h \right)$$ can be used for simulating soil moisture of wetting branch during infiltration and irrigation processes at soil water pressure heads lower than ‒1000 mbar and a near of saturation for agrosoddy-podzolic soil of silt loam and silty clay loam textures.