Biosolids and chemical fertilizer application on the Chihuahuan desert grasslands

Sewage sludge or biosolids refers to the solids removed from municipal waste water during treatment. Currently, sewage sludge is used to refer to untreated material, while biosolids refers to treated material., There are several estimates as to how much sewage sludge is currently produced or will be produced in the U.S. in the future. On average, a typical person generates 16.9 liters of sewage sludge per week (Chermisinoff, 1993). According to the U.S. Environmental Protection Agency (USEPA, 1989) approximately 6.5 million dry tons of sewage sludge are generated annually, and this is expected to increase to approximately 13 million dry tons by the year 2000.

Due to the large quantities of sewage sludge generated, management of treated sewage sludge, or biosolids, is becommg increasingly important. The Marine Protection Research and Sanctuary Act of 1988 banned ocean dumping of biosolids as a disposal technique, leaving only land filling, incineration, and land application. Land filling is facing increased regulations because of ground water pollution and decreases in available land fill space. Incineration is also plagued with problems, such as air pollution, high energy input, and capital costs. Land application is a promising alternative to ocean dumping.

Land application is defined as the spreading of biosolids on or just below the soil surface, and is becoming a widely used sludge management option. Land application is divided into four categories: agricultural use, forest lands, land reclamation, and land dedicated to sludge application. Land application is encouraged by the EPA wherever environmentally feasible (USEPA, 1989). Land application has been beneficially used on croplands, forest lands, and reclaimed mines throughout the U.S. However, land application has not been widely studied in the arid and semi-arid southwest or on native rangelands. The desert southwest, including the Trans-Pecos region of Texas, receives low and unpredictable rainfall and has high temperatures, high evaporation rates, and low organic matter contents in the soil All of these factors limit native plant growth on rangelands. Application of biosolids might ameliorate some of these conditions by providing organic matter to the soil and reducing soil water evaporation. In addition, biosolids contains several plant macro- and micro- nutrients such as nitrogen, phosphorus, copper, manganese, and zinc that can increase plant production. As long as biosolids do not cause detrimental effects in this semi-arid environment, the Trans-Pecos is an excellent area for land dedicated to sludge application for several reasons: vast acreages of available land, and few estimated number of days when biosolids can not be applied because of unfavorable weather (precipitation) (USEPA, 1989).