Sewage Sludge Application in Semiarid Grasslands: Effects on Vegetation and Water Quality

The effects of municipal sewage sludge (45 Mg ha-1 oven dry weight basis, surface-applied) on semiarid rangeland in central New Mexico were studied over a two-year period. Sewage sludge application increased total nitrogen (TKN) and extractable ammonium (NH4-N), nitrate (NO3-N), and phosphorus (P), but did not significantly increase soil organic carbon (OC) in the mineral soil underlying the applied sludge. Extractable soil copper (Cu), lead (Pb), and zinc (Zn) increased significantly following sludge application, but remained at low concentrations (<4.0 mg kg-1) well below established regulatory standards. Soil cadmium (Cd) levels remained below detection limits.

Above-ground plant cover on treated plots increased following the sludge application, but only in response to rainfall. Root growth was significantly less on treated plots. Above-ground plant tissue from sludge-treated plots had significantly greater TKN and Cu.

Results from natural storms and rainfall simulation experiments showed that surface-applied sludge significantly reduces surface runoff and total sediment yield. Given the immediate reductions in runoff and total sediment yields and the favorable vegetative response to the added sludge, surface application of municipal sewage sludge to semiarid rangelands has the potential to reduce deleterious runoff and sediment from Southwestern rangelands.