Heavy metals in soil after sewage sludge application. II - Availability

The use of industrial and city wastes with high heavy metal contents in agriculture have increased the need for obtaining the concentration of such elements that are available in the soil. Thus, a greenhouse experiment was carried out at the FCAV-UNESP, in Jaboticabal, Sao Paulo State, Brazil in order to compare analysis methods (DTPA, HCl 0.1 mol L-1, Mehlich-1, and Mehlich-3) to evaluate the Cu, Mn, Ni, Pb, and Zn availability for corn (Zea mays L.) plants in two soils (an Eutrustox and a Ultipsamment). A complete randomized design with three replications of treatments in a 2 x 2 x 5 factorial arrangement (two soils, presence or absence of lime, and five sewage sludge rates) was used. In the limed treatments the soils were amended with agricultural lime to raise the soil pH (CaCl2) to 5.3. The sewage sludge rates (dry weight basis) were equivalent to 0, 10, 20, 40, and 60 t ha(-1). All the extractants tested proved inefficient to evaluate availability of all metals concurrently. The inclusion of the soil pH in the regression models significantly improved the relationship between the amounts of Mn accumulated in the shoot and those extracted with DTPA, HCl 0.1 mol L-1, Mehlich-1, and Mehlich-3.