APPLICATION OF BIOSOLIDS TO DEGRADED SEMIARID RANGELAND - 9-YEAR RESPONSES

Rangeland restoration through surface application of biosolids (munici pal sewage sludge) is an increasing practice. Biosolids supply both or ganic matter and available nutrients that are lacking in degraded rang eland soils. This study investigated the effects of biosolids applicat ions of 0, 22.5, 45, and 90 Mg ha(-1) to a degraded rangeland in 1985 on the soil chemical properties and N mineralization potentials 8 and 9 yr after the application, respectively. Following an initial increas e in proportion to the application rate, levels of water-extractable C a, Mg, Na, nitate (NO3-N), and electrical conductivity declined to tha t near the control soils after 8 yr. Nearly all diethylenetriaminepent aacetic acid (DTPA)-extractable metals (Fe, Zn, Cu, Cd, and Pb) were h ighest in the collection 4 Sr after application but were near concentr ations in the control soil after 8 yr. Nitrogen mineralization potenti als were significantly higher (P < 0.05) in the 45 and 90 Mg ha(-1) ap plications after 9 yr, indicating that site fertility remained higher even though most soil chemical properties were returning to untreated levels.