Phytoavailability and extractability of copper and zinc in calcareous soilamended with composted urban wastes

A greenhouse experiment was conducted under simulated field conditions usin g large-capacity plastic pots, filled each one with 25 kg of air-dried calc areous soil. Besides the control, four treatments were prepared by applying separately two rates (20 and 80 Mg ha(-1)) of municipal solid waste (MSW) compost, and co-composted municipal solid waste and sewage sludge (MSW-SS). Lettuce was planted and harvested 2.5 months later. The application of com posted urban wastes tended to increase Cu concentration in lettuce with res pect to the control, but it was only significant when the higher rate of MS W compost was applied. The control showed values of Zn concentration in pla nt within a deficient range. In general, composted urban wastes treatments had increased Zn concentration values, which were within the sufficiency ra nge. Both treatments with MSW compost increased Cu and Zn uptake in compari son with MSW-SS co-compost treatments. At the postharvest, all composted ur ban wastes treatments increased significantly DTPA-extractable Cu content i n soil with respect to the control; it was also significant the increase in AAAc-EDTA-extractable Cu in soil produced by the addition of the higher ra te of MSW compost. The application of composted urban wastes increased sign ificantly DTPA-extractable and AAAc-EDTA-extractable Zn contents in soil ve rsus the control, except for the lower rate of MSW-SS co-compost. The value s of DTPA-extractable/total ratio for Cu and Zn were under 10%, except for the treatment applying the higher rate of MSW compost which promoted higher values. The values of AAAc-EDTA-extractable/total ratio for Cu were above 10% in all treatments including the control. This tendency was also observe d in AAAc-EDTA-extractable/total ratio for Zn when applying both rates of M SW compost or the higher rate of MSW-SS co-compost.