Arid and semiarid rangelands are suitable for responsible biosolids application. Topical application is critical to avoid soil and vegetation disturbance. Surface-applied biosolids have long-lasting effects in these ecosystems. We conducted a 10-year research program investigating effects of biosolids applied at rates from 0 to 90 dry Mg？ha？1 on soil water infiltration; runoff and leachate water quality; soil erosion; forage production and quality; seedling establishment; plant physiological responses; nitrogen dynamics; biosolids decomposition; and grazing animal behavior and management. Biosolids increased soil water infiltration and reduced erosion. Effects on soil water quality were observed only at the highest application rates. Biosolids increased soil nitrate-nitrogen. Biosolids increased forage production and improved forage quality. Biosolids increased leaf area of grasses; photosynthetic rates were not necessarily increased by biosolids. Biosolids effects on plant establishment are expected only under moderately favorable conditions. Over an 82-mo exposure period, total organic carbon, nitrogen, and total and available phosphorus decreased and inorganic matter increased. Grazing animals spent more time grazing, ruminating, and resting in biosolids-treated areas; positive effects on average daily gain were observed during periods of higher rainfall. Our results suggest that annual biosolids application rates of up to 18？Mg ha？1 are appropriate for desert rangelands. 1. Introduction Wastewater treatment produces liquid effluent and sewage sludge. When sewage sludge is further treated for pathogen control (e.g., with anaerobic digestion or composting) the resulting product is called “biosolids.” Dewatered biosolids typically have 60%–80% water content and contain a broad variety of micro- and macronutrients; about 60% of the solids content in biosolids is organic matter [1]. The US currently produces approximately 7.1 million metric tons of biosolids annually [2]. Disposal options include incineration and processing for energy recovery, landfill disposal, and land application [2]. The US EPA regulates and encourages land application both in agronomic settings and on rangelands. In fact, about 50 to 60% of annual biosolids production is used in land application [3, 4]. Land application on rangelands, especially semiarid rangelands, is particularly attractive because the climate of these ecosystems typically allows for year-around application; additionally, distance from urban areas, wide-open spaces, and large acreages in private holdings make
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