This study was designed to evaluate the effect of the successive applications i crescent doses, of two sources of sewage sludge on the total contents of Cu, Mn, Ni, Pb and Zn in soil, in three successive crops of corn. The experiment was conducted in the experimental field of Embrapa Environment, located in Jaguariúna in São Paulo state over the agricultural years of 1999/2000 and 2000/2001 in a Diostroferic Red Latosol. The sludges utilized in the experiment were obtained in the Sewage Treatment Stations (STSs) of Franca and Barueri. The treatments for each source of sewage sludge were the following: control, without addition of sewage sludge; NPK; application of sewage sludge aiming to supply the amount of N normally required by corn; 2, 4 and 8 times the rate of sludge applied in the 1N treatment. The rates of sludge applied (dry basis) ranged from 0 to 139.24 Mg ha-1 for Barueri sludge and from 0 to 80.27 Mg ha-1 for Franca sludge. The accumulation of Cu, Mn, Ni, Pb and Zn through the determination of the total content (regia water) of these metals in soil were evaluated. The total contents of soil Cu and Zn increased with the increment of applied doses of the two sludge sources, however, were not verified in soils, total contents of the heavy metals analyzed above the values established in literature for agricultural soils.
Heavy metals; chemical extractor; organic residue; corn fertilization