To derive PTFs in clay soils Kurdistan

The soil unsaturated zone plays a significant role in hydrological cycle. One of the most characteristics of this zone, is the soil water retention curve that its parameters is needed as input in most of studies for determining hydraulic specification of the soil. One of the indirect method is the Pedo-Transfer function which contains a complex of regression equations to relate easily obtainable soil properties to its missing soilcharacteristics. In most parts of the world including Iran clay soil are found very much. These kind of soil own a very good power of fertility but their hydraulic functionscharacters such as swelling and preferential flow cause to them have been studied less. The goal of this study, is to produce Pedo-Transfer functions of this soils by the using of easily obtainable soil properties. 25 soil samples with day texture from Kordestan were gathered randomly. The particle size distribution, bulk density, calcium carbonate percentage were determined. The soil water retention curves for the entire range of interest were obtained using the pressure plate apparatus. For the separation of PTFs, independent variables were divided in to two groups. The first group include the particle size distribution, bulk density and calcium carbonate percentage. In second group, geometric diameter, geometric standard deviation, bulk density and calcium carbonate percentage were settled. From the independentvariables, the best subset for evaluating specific point of soil water retention curve were selected by the acid of regression method. For two groups, regression formulas were achieved as multiple linear form. Results show that there is a suitable attention for evaluating the relations for the assess mint of soil water retention curve of the soil for application goals.