USE OF COAL BED NATURAL GAS (CBNG) WATERS: SOIL AND PLANT RESPONSES
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With about 20,000 coal bed natural gas (CBNG) wells currently permitted or drilled in the Powder River Basin (PRB) of Montana and Wyoming and projections of more than 50,000 future wells, CBNG water production in the PRB over the next 15 years will exceed 366,000 ha-m. Therefore, proper CBNG product water utilization is warranted. Land application using conventional center-pivot and side-roll irrigation systems is a common strategy for managing saline-sodic waters derived from CBNG production within the PRB. Various soil and plant impacts resulting from 1 to 4 years of saline-sodic water (EC = 1.8 to 4.0 dS m -1; SAR =15 to 38) applications were examined during the 2003 and 2004 field seasons on 6 (2003) to 8 (2004) study sites representing native range grasslands, seeded grass hayfields and alfalfa hayfields. Because soil and plant types, water application rates and water and soil treatment strategies were variable across study sites, parameters measured from each treated (irrigated) site were compared directly to those from representative control (non-irrigated) sites. Soil chemical and physical parameters including pH, EC, SAR, texture, bulk density, surface infiltration rate and Darcy flux rates were measured at various depth intervals to 120 cm. Multiple year applications of saline-sodic water produced consistent trends of increased soil EC and SAR values at depths to 30 cm, reduced surface infiltration rates and reduced Darcy flux rates to 120 cm. Significant (P=0.05) differences in EC, SAR, infiltration rates and Darcy flux (P=0.10) were determined at most sites. Up to 4 years of saline-sodic water applications significantly (P=0.05) increased native perennial grass biomass production and cover on treated vs. control sites. However, overall species evenness was reduced. Biological effects were variable and complex, reflecting site specific conditions and management strategies.