Application of biosolids to degraded semiarid rangeland: Nine-year responses

Rangeland restoration through surface application of biosolids (municipal sewage sludge) is an increasing practice. Biosolids supply both organic matter and available nutrients that are lacking in degraded rangeland soils. This study investigated the effects of biosolids applications 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 increase in proportion to the application rate, levels of water-extractable Ca, Mg, Na, nitate (NO3-N), and electrical conductivity declined to that near the control soils after 8 yr. Nearly all diethylenetriaminepentaacetic acid (DTPA)-extractable metals (Fe, Zn, Cu, Cd, and Pb) were highest in the collection 4 Sr after application but were near concentrations in the control soil after 8 yr. Nitrogen mineralization potentials were significantly higher (P < 0.05) in the 45 and 90 Mg ha(-1) applications after 9 yr, indicating that site fertility remained higher even though most soil chemical properties were returning to untreated levels.