Spatial Variability of Soil Properties In An Arid Ecosystem Irrigated with Treated Municipal and Industrial Wastewater.

Knowledge of spatial variability of soil properties is important for designing site specific management practices for soil affected by different anthropogenic activities. Study was conducted at West Mesa land application site to determine the degree of spatial variability of soil physical and chemical properties and suggest sustainable management strategy to reduce the detrimental effect to the native ecosystem. Bulk and core soil samples were collected at 0-20 cm depth from 54 grids (50 X 50 m) and additional 20 samples were collected at smaller grids during March 2009. Soil properties analyzed were; field capacity (FC), wilting point (WP), available water content (AWC), hydraulic conductivity (K_s), soil texture, bulk density (BD), pH, nitrate (NO₃^-), chloride (Cl^-), organic matter (OM), and sodium adsorption ratio (SAR). GS+ software was used to obtain semi-variograms and cross- variograms. The SAR, Cl^-, WP, K_s, NO₃^- were most variable with CV>0.35. FC, AWC, silt and OM were moderately variable (0.15<CV0.35) whereas sand; clay, BD, and pH were least variable (CV<0.15). Moran’s I statistics indicated that soil physical properties were auto-correlated up to the lag distances of 25 m and soil chemical properties at a lag distances of 50 m. Cross-variogram showed that SAR was spatially correlated with K_s and sand content, K_s with BD, therefore kriging or cokriging can be used to estimate K_s from bulk density. Kriged spatial distribution maps showed positional similarity and most of the higher chemical properties were concentrated in the northeast and southwest portion and lower near the center of the experimental field. Average SAR concentration in the northeast and southwest portions of the field was (> 15) which is the threshold limits for most of the plants. So it is necessary to monitor SAR on a regular basis and change the wastewater application pattern with more wastewater application in the middle and less in the northeast and southwest part of the experimental site.