Determination of unsaturated soil hydraulic properties at different applied tensions and water qualities

Irrigation with low-quality water may change soil hydraulic properties due to excessive electrical conductivity (ECw) and sodium adsorption ratio (SAR(w)). Field experiments were conducted to determine the effects of water quality (ECw of 0.5-20 dS m(-1) and SAR(w) of 0.5-40 mol(0.5) 1(-0.5)) on the hydraulic properties of a sandy clay loam soil (containing similar to 421 g gravel kg(-1) soil) at applied tensions of 0-0.2 m. The mean unsaturated hydraulic conductivity [K(psi)], sorptive number (alpha) and sorptivity coefficient (S) varied with change in ECw and SAR(w) as quadratic or power equations, whereas macroscopic capillary length, lambda, varied as quadratic or logarithmic equations. The maximum value of K(psi) was obtained with a ECw/SAR(w) of 10 dS m(-1)/20 mol(0.5) 1(-0.5) at tensions of 0.2 and 0.15 m, and with 10 dS m(-1)/10 mol(0.5) 1(-0.5) at other tensions. Changes in K(psi) due to the application of ECw and SAR(w) decreased as applied tension increased. Analysis indicated that 13.7 and 86.3% of water flow corresponded to soil pore diameters <1.5 and >1.5 mu m, respectively, confirming that macropores are dominant in the studied soil. The findings indicated that use of saline waters with an EC of <10 dS m(-1) can improve soil hydraulic properties in such soils. Irrigation waters with SAR(w) < 20 mol(0.5) 1(-0.5) may not adversely affect hydraulic attributes at early time; although higher SAR(w) may negatively affect them.