Establishing Soil Hydraulic Properties for Tunisian Soils Using Common Pedotransfer Functions

Soil hydraulic properties are essential for numerical models that simulate water flow and solute transport in the vadose zone. Actually Tunisian soils lack of a database that includes the main values soil retention properties and soil saturated hydraulic conductivity. The objective of this study is to establish the first database of soil hydraulic properties based on open access data and pedotransfer functions (PTFs). For this purpose, the harmonized soil database (FAO) is used to locate 752 measurement points in Tunisia and then to determine the soil texture, the organic carbon content, and the bulk density in each point. The obtained values were introduced as input in the CalcPTfs software to estimate the soil retention parameters of the van Genuchten’s equation (van Genuhten, Van Genuchten, M. T. (1980). A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal, 44, 892–898.): the residual volumetric soil water content (θr), the volumetric soil water content at saturation (θs), and the two shape parameters α and n. The soil saturated hydraulic conductivity is obtained based on two widely used pedotransfer functions (Saxton et al., Saxton, K. E., Rawls, W. J., Romberger, J. S. & Papendick, R. I. (1986). Estimating generalized soil water characteristics from texture. Transactions of the ASAE, 50, 1031–1035.; Schaap et al., Schaap, M. G., Leij, F. J., Genuchten, & Van Rosetta v1.2, M. T. (2001). A computer program for estimating soil hydraulic parameters with hierarchical pedotransfer functions, 251, 163–176.). The results allowed the establishing of a catalogue that include the values of soil retention parameters and soil hydraulic properties of each soil texture class based on the United State Department of Agriculture (USDA) classification. Also, the significance of the difference between each value obtained from the PTFs functions was studied by Tukey test at 5% level. Thus, the soil hydraulic properties catalogue can be simplified since the difference between the values of some PTFs functions was not significant. In conclusion, the important database of the soil hydraulic properties established may have a various application in agricultural, hydrological. and environmental studies in Tunisia for the decision makers and for research purposes.