ايجاد توابع انتقالي نقطه اي براي منحني رطوبتي خاك هاي گچي

Predicting Water Retention Curve of Gypsiferous Soils Using the Derived Point Pedotransfer Functions

The parametric description of the soil water retention curve is crucial to study water movement and solute transport in the unsaturated soil. Despite the progresses made on direct measurement of the hydraulic properties, the majority of these techniques remained relatively time consuming and costly. Further, due to inherent temporal and spatial variability of these hydraulic characteristics in the field conditions, large number of samples is required to properly characterize area of land. An alternative was then, the use of so-called Pedotransfer Functions (PTFs) that enabled to estimate difficult soil characteristics from easily obtainable soil properties. In arid and semi-arid areas, gypsum is a major solid component of the soil that influences the soil hydraulic properties. The objective of this study was to derive some Pedotransfer Functions to predict the water retention curve of some Gypsiferous soils. Consequently, 35 soil samples with gypsum content ranging from 3.8 to 32.7 percent were collected. The gypsum content was measured by Acetone method, the bulk density by volumetric method, the particle size distribution by covering the particles with Barium Sulfate. The soil water retention curve was obtained, using pressure plates apparatus. The easily obtainable variables were grouped into two groups (i) particle size distribution, bulk density and gypsum content, (ii) bulk density, gypsum content, geometric mean and geometric standard deviation of particle diameter. The stepwise linear regression method was used to derive the PTFs. Two types of point PTF functions were derived, using these variables. Comparison of the results indicated that the first group of variables had better prediction of water retention than the second group. The gypsum content appeared to be the second dominant parameter to predict the water retention at 0, -33, -100, -300, -500 and -1500 kPa.