ESTIMATING HYDRAULIC PROPERTIES OF SOME SOIL SERIES OF SINDH
Keywords:HYDRUS-1D, soil series, soil water retention curve, VGM parameters
Quantitative description of soil hydraulic properties is necessary for determining the soil water holding capacity, infiltration, percolation, and runoff rates and for modelling water and solute transport in the vadoze zone. Recognizing the key role of soil hydraulic properties in the management of irrigation scheduling, salinity and agricultural drainage, a study was conducted to determine hydraulic properties of the five soil series, commonly found in Sindh, through laboratory method and numerical modeling. Six free drainage experiments were carried out in the laboratory using Jhakkar, Matli, Miani, Sarhad and Sultanpur soil series to estimate their hydraulic properties. Oven dried soil samples of each soil series were filled in 15 plastic pipes of diameter 15 cm and length 30 cm with holes at the bottom for free drainage. Natural soil density and porosity was maintained in pipes by compaction. Tensiometers were installed in the center of each pipe and then pipes were filled with water up to saturation level. Loss in weight of soil filled pipe was measured by weighing and the corresponding tensiometeric reading was recorded. Soil water retention curves were thus drawn from the recorded data. HYDRUS-1D model was used to optimize the van Genuchten-Mualem (VGM) parameters from the physical properties of the considered soil series. To assess the reliability of the model, measured water retention curves were fitted with the predicted curves with HYDRUS-1D model. The measured and predicted soil retention had a strong relationship with the coefficient of determination (R2) ranging from 0.90 to 0.98. Based on the study, it is concluded that HYDRUS-1D model is a robust tool for determining the hydraulic properties of soil series commonly found in Sindh rather than determining through field methods which are laborious, expensive and time consuming.
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