Prediction of Some Hydraulic Properties of Calcareous Soils of Bajgah Region Fars Province Using Regression Pedotransfer Functions

Document Type : Research Paper

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Hydraulic attributes play important role in hydrological studies, soil conservation, designing irrigation and drainage systems, soil conservation, and controlling soil erosion in watersheds. Their measurements are very tedious and time consuming and due to high spatial variability, a large number of measurements are required for obtaining reliable values. Nowadays, prediction of these attributes from the easily available soil properties has received increased attention. Therefore, the presentstudy aimed to introduce pedotransfer functions (PTFs) for estimation of some hydraulic coefficients in calcareous soils of Bajgah region in Fars province. In 100 sites, soils attributes including saturated and near saturated hydraulic conductivity, sorptivity coefficient, and hydraulic diffusivity were determined using Single Ring and Droplet methods and easily available soil properties including  sand, silt, clay, bulk density, soil moisture, pH, calcium carbonate, gypsum, cation exchange capacity and sodium adsorption ratio were measured. Pedotransfer functions were derivate using stepwise multivariate regression method and were evaluated by calculating some statistical measures. In prediction of soil hydraulic attributes, easily available physical properties, i.e. sand content, geometric mean diameter of aggregate and soil particles, and saturated volumetric content as well as easily available chemical properties i.e. pH, organic matter, calcium carbonate equivalent, gypsum, total dissolved solids, cation exchange capacity and sodium adsorption ratio were entered in PTFs as estimator. The introduced PTFs could predict hydraulic soil attributes precisely with coefficient of determination of 0.31 and 0.92 and index of agreement of 0.47 and 0.97 for hydraulic diffusivity (the lowest accuracy) and sorptivity coefficient (the highest accuracy), respectively. Due to tedious and time consuming nature of measurement of these attributes and the easy availability of the applied properties, the introduced PTFs can be used for prediction of these hydraulic attributes in the studied area as well as in other similar regions. Of course, to use these PTFs in other regions, the equations should first be locally tested and calibrated.

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