USE OF AEROBICALLY DIGESTED, ANAEROBICALLY DIGESTED AND LIME STABILIZED BIOSOLIDS FOR RESTORING SEMI-ARID RANGELANDS

Biosolids land application was demonstrated to be a potentially cost effective approach for restoring the environmental health and forage productivity of marginal and/or disturbed western rangelands. By land applying aerobically digested, anaerobically digested and lime stabilized biosolids at rates significantly greater than the estimated agronomic rate, forage dry matter yields were found to increase significantly compared to control plots. Although, in general, dry-matter forage yields increased commensurate with the increase in biosolids land application, the increase in the lime-stabilized biosolids application rate above the agronomic rate resulted in a decrease in forage yield.An explanation for the inverse relationship observed between forage yield and biosolids application rate for lime stabilized biosolids was unclear. Several possible explanations included the following: 1) increased application of calcium-based salts was toxic to rangeland vegetation, 2) the large amount of biosolids applied physically obscured sunlight thereby reducing the emergence of rangeland vegetation and 3) high pH of lime stabilized biosolids reduced the availability of plant micronutrients (e.g., metals).Deep soil sampling results confirmed that nitrate leaching can be significant when land applying biosolids at rates considerably greater than the agronomic rate. However, in arid or semi-arid regions where the rate of evapotranspiration far surpasses the precipitation rate and/or groundwater depths are considerable, nitrate leaching may have a negligible impact on groundwater quality. While nitrate levels increased with soil depth, concentrations of plant available phosphorus decreased with soil depth. Because of its association with surface soils, mitigation of potential environmental impacts associated with phosphorus requires implementation of rangeland management practices that minimize soil erosion.Finally, forage grown on rangelands amended with biosolids was observed to have both greater dry matter yields and nutritional values. Crude protein and the relative feed value of forage harvested from rangelands amended with biosolids were significantly greater than the forage grown on control sites. Given the economic benefit associated with increased vegetative yield and forage nutritional value in animal production, biosolids land application is a rangeland restoration approach that should receive greater consideration in support of sustainable ranching practices.