The application of sludges, especially sewage-sludge (SS) to agricultural soils is one of the most rational ways of using this residue. The purpose of this study was to investigate the effect of SS on some chemical properties of an SS-amended Ultisol under sugarcane (variety RB 855536) for two years; from October 2002 to August 2003 - growing season 2003/04 and from October 2003 to October 04, designated 2004/05 crop season. Eight treatments were evaluated: (a) control; (b) Mineral fertilization (120 kg ha-1 N+150 kg ha-1 K2O); (c) LE + 0N, incorporated into soil just after application (ISA); (d) LE + 0N, incorporated into soil 60 days after application (IS60A); (e) LE + 60 kg ha-1 N (ISA); (f) LE + 60 kg ha-1 N (IS60A); (g) LE + 120 kg ha-1 N (ISA); h) LE + 120 kg ha-1 N (IS60A). The SS was obtained from a biologic and aerobic municipal sewage treatment plant and the application rate was based on nitrogen mineralization rate (28 %) and sugarcane N requirement (120 kg ha-1). The soil was sampled in the 0-20 cm layer and analyzed for pH, C, available P, exchangeable K, Ca and Mg, DTPA pH 7.3 extractable Cu, Fe, Mn and Zn, total Cd, Cr, Ni, and Pb content. Sugarcane leaves were collected at the age of 4.5 months and analyzed for P, K, Ca, Mg, Cu, Fe, Mn, Zn, Cd, Cr, Ni, and Pb. SS application resulted in higher soil C levels in the second study period. The IS60A treatment resulted in a higher soil C content, probably due to SS dehydration and the reduced contact with soil particles. The other soil attributes (pH, available P and exchangeable K, Ca and Mg) were not affected by residue application. Besides, the SS treatments resulted in a higher P leaf content, indicating SS as a reasonable P source. The metal and nutrient contents in soil and leaves were within a range considered adequate, even under successive SS applications. Despite the heavy metal application to the soil through SS, no increase in Cd, Cr, Ni and Pb contents was observed in the soil or in sugarcane leaf concentrations.
biosolid; heavy metal; macronutrient; micronutrient; plant nutrition
