Spatial Variability of Infiltration Rate and Sodium Content of Desert Soils: Implications for Management of Irrigation Using Treated Wastewater.

Information on soil hydraulic properties, their spatial variability and relation to soil chemical properties is crucial for making management decisions for lands affected by anthropogenic activities. In situ infiltration tests were conducted at West Mesa land application site to determine the spatial variability of infiltration rate using tension infiltrometer and to suggest suitable management strategies to reduce the detrimental effect to the soil and plant environment. Infiltration tests were conducted for an hour at 50 x 50 m grid spacings and at 0, 5-, 10-, 20-, and 30-cm tensions during March-April 2009. Woodings’s equation was used to calculate near saturated (K_s) and unsaturated hydraulic conductivity (K (Ψ)) from the steady state infiltration rate (I_s). Bulk soil samples were also collected from each grid locations at 0-20 cm depth to determine sodium (Na⁺) before the infiltration test. Study area was divided into five classes with K_s increasing from class I to V; class I contained K_s ≤ 5 cm h^-1, class II 5.1 < K_s ≤ 10 cm h^-1, class III 10 < K_s ≤15 cm h^-1, class IV 15.1< K_s ≤20 cm h^-1 and, class V K_s > 20 cm h^-1. Coefficient of variation (CV) showed that different K_s classes were low to moderately variable and semivariogram displayed both short and long range variability. K_s kriged map showed classes I, II and III were concentrated at northeast and southwest side of the study site where higher Na⁺ was detected and classes IV and V were at the center of the study site where lower Na⁺ level was detected. Significant lower numbers of macropores and smaller macropore radius were observed in the area of lower K_s and higher Na⁺ concentrations. Therefore, further increase in Na⁺ can further decrease the K_s and macroporosity and may affect the water uptake by the native vegetation. It is necessary to change the wastewater application pattern, lower wastewater in the southwest and northeast portion and higher in the center of the study plot.