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Restoration of degraded rangelands to improve forage productivity and reduce soil erosion remains an ecological and environmental priority for western US states. Biosolids land application represents a potentially cost effective approach for improving the ecological health and productivity of marginal and disturbed rangelands. The US Environmental Protection Agency (EPA) Region VIII (Denver, CO) in conjunction with the Utah Division of Water Quality (Salt Lake City, UT) and Utah State University (Logan, UT) has implemented a series of field demonstrations aimed at evaluating the potential benefits of land applying aerobically digested and lime stabilized biosolids to restore disturbed rangelands in Tooele County, UT.

Biosolids land application at rates significantly greater that the estimated agronomic rate was observed to increase vegetative biomass production above that which was observed for control plots. For example, while the control plot recorded an average vegetative growth of 366.6 lbs per acre (wet basis), plots receiving lime-stabilized biosolids at 10X the agronomic rate and aerobically digested biosolids at 20X the agronomic rate reported maximum biomass yields of 2043.7 and 1688.0 lbs per acre (wet basis), respectively. Preliminary ecological analysis indicated that the dominant plant species found on the control test plots was Bromus tectorum (cheat grass) while the dominant vegetative species found on the sites amended with biosolids was Hordeum marinum gussoneanum (seaside barley).

Soil sampling indicated that nitrate concentrations in all test plots including control increased with increasing soil depth. While the control plots had nitrate concentrations that ranged from 7.5 mg/kg (at 0.75 feet below the ground surface) to 88.0 mg/kg (at 5.0 feet below ground surface), soils amended with biosolids were found to have soil nitrate concentrations that ranged from 12.0 mg/kg (at 0.75 ft below the ground surface) to as high as 183.6 mg/kg (at 5.0 feet below ground surface). The increase in soil nitrate levels was expected since biosolids were applied at rates that were either equal to or significantly greater than the agronomic rate.

In general, soil ammonia concentrations in all biosolids land application test plots were found to be statistically equivalent to the control plots. This observation was not surprising as the alkaline soil conditions would facilitate ammonia volatilization. The only exceptions to this behavior was observed in lime stabilized and aerobically digested biosolids test plots that received 10X and 20X the estimated agronomic rate, respectively. At a measured soil depth of 0.75 feet, the ammonia concentrations at these sites were much larger than that observed within the control. These observations suggest the possibility that ammonia mass transfer limitations associated with unassimilated land applied biosolids may exist.

Finally, like nitrate, salt concentrations (as measured by electrical conductivity) were found to increase with increasing depth. Since salt concentrations are dependent on moisture movement within the soil profile, the future rate, extent and direction of salt movement within the test plots will ultimately depend on the level of precipitation relative to evapotranspiration.
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Document Type: Research Article

Publication date: 01 January 2006

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