Spatial Variability of Soil Properties in an Arid Ecosystem Irrigated With Treated Municipal and Industrial Wastewater

Information on spatial variability of soil properties is important for designing site-specific management practices for soils affected by human activities. Spatial variability study was conducted at West Mesa near Las Cruces, New Mexico, to identify the areas where remediation is needed and suggest sustainable management strategies to reduce the effect of treated saline and sodic wastewater application on soil environment and existing native vegetations based on the spatial variability of soil physical and chemical properties. Bulk and core soil samples were collected from the center of 54 (50 x 50 m) grid points, and additional 30 samples were collected from smaller grids at 0- to 20- and 20- to 40-cm depth during summer 2010. Geostatistical software (GS+) was used to obtain semivariograms and cross-variograms. Coefficient of variation (CV) indicated that sodium adsorption ratio (SAR), chloride (Cl-), wilting point, saturated hydraulic conductivity (K-s), and nitrate (NO3-) were most variable with CV of greater than 0.35, whereas sand, clay, bulk density, and pH were least variable (CV <0.15). Cross-variogram showed that SAR was spatially correlated with K-s and sand content; K-s, with bulk density; therefore, kriging or cokriging can be used to estimate SAR from K-s. Blocked kriged spatial distribution maps showed positional similarity, and most of the higher chemical properties were concentrated in the northwest and southeast portion and lower near the center of the experimental field. Average SAR concentration in the northwest portion was 22.77, and a southeast portion of the field was 18.12, which were above the threshold limits (>15) for most 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 northwest and southeast part of the experimental site.