The hydraulic properties of a sandy soil treated with gel-forming soil conditioner

The irrigated sandy soils in the arid regions have limited water retention capacity. A laboratory study was conducted on a sandy soil to investigate the effect of a gel-forming soil conditioner (Jalma) on the soil water retention relationship (ψ-θ), soil water diffusivity (D(θ)), and saturated hydraulic conductivity (K_S). Zero, 0.2, 0.4, and 0.8% of Jalma (J) were uniformly mixed with a sandy soil (Typic Torripsamments). The soil water distribution, horizontal wetting front advance (X), and infiltration (I) were measured. The results indicate: (1) the available water content increased exponentially with increasing J, but K_S decreased exponentially with increasing J; (2) the X and I decreased with increasing J, and their relationships with time can be described by power functions; (3) the D(θ) increased with increasing θ and decreased with increasing J. Two approaches were taken to calculate K(θ) by using: (1) the D(θ) functions and the complete θ-ψ relationship, and (2) the measured K_S and a limited range of the θ-ψ relationship. The two approaches were found to be comparable, but the second approach is recommended since it required simpler and available data. The calculated K(θ) increased with increasing θ and decreased with increasing J. Generally, this study revealed that the addition of gel-conditioner improved the hydraulic properties of sandy soil and that the best rate of Jalma is 0.4%. This addition rate limited deep percolation losses while maintaining adequate infiltration and water retention characteristics.