Cumulative soil chemistry changes from land application of saline-sodic waters

Management of large volumes (60,000 ha-m) of co-production water associated with coal bed natural gas (CBNG) water extraction is a potential concern in the Powder River Basin (PRB) of Wyoming and Montana due to elevated water salinity and sodicity levels. Land application of saline-sodic CBNG water is a common water management method being practiced in the PRB, which can result in deterioration in soil quality. The objective of this study was to evaluate effects from 1 to 4 yr of land application with CBNG water on soil chemical properties at six study sites (fine to loamy, mixed to smectitic, mesic, Ustic Ardisols and Entisols) in the Wyoming PRB region. Changes in chemistry of soils collected from six depths irrigated with CBNG water were compared with representative nonirrigated soils. Applications of CBNG water significantly increased soil EC, SAR, and ESP values (up to 21, 74, and 24 times, respectively) compared with nonirrigated soils. Differences in soil chemical properties between an irrigated and nonirrigated coarse-textured soil were less than that of fine-textured soils, emphasizing texture as an important factor for salinity buildup. Pretreatment of CBNG water using a sulfur burner and application of gypsum and elemental S soil amendments reduced soil pH but did not prevent the build-up of salts and sodium. Study results suggest that current CBNG water management strategies are not as effective as projected. Additional research is needed to develop management strategies appropriate for mitigating adverse effects of CBNG water irrigation.