Comparison of Unsaturated Hydraulic Conductivity Calculated by Jackson Equation and Van Genuchten Equation for Three Different Soils in Their Gypsum Content and Treated with Polymer and Peatmoss

Abstract

An experiment was conducted to compare the unsaturated hydraulic conductivity (K) calculated by Jackson equation and van Genuchten equation for soils different in gypsum content and treated with some soil conditioners. Two soils were used, gypsiferous soil (410 gm kg-1gypsium) and clayey soil (435 gm kg-1 clay), were mixed in three levels 0, 50, and 100%. The soils were treated with peat moss 0 and1%, polymer,0,1.and 2% and without addition. Then, were packed into plastic tubes 5 cm diameter and 25 cm in height at bulk density of 1.3 Mg m-3 and were exposed to three wetting / drying cycles. The unsaturated hydraulic conductivity was calculated from (Jackson equation, and van Genuchten equation. the results showed good agreement between K values measu dy using Jackson and van Genuchten equation using RETC program. The relationship between K and θ and percentages of gypsum is a positive and between K and ψ an inverse relationship. The value of K increased from 81.7 cm. day-1 to 137.8 cm. day-1 when the percentage of gypsum was increased from 46 to 410 g kg-1 consecutively for soil in treated with conditioners and within minor tension limits approaching zero. The K values decreased when the soil was treated with peatmoss and polymer, and the most effective treatment in reducing the K values was a mixture of (2% polymer + 1% peatmoss). The K values remained close to zero with medium to high tensions and also with medium to low θ, and it did not increase to an effective degree except when θ approached its upper limits and with low tensions, and its increase was exponential within these ranges.