This study was carried out in order to evaluate yields of wheat, lettuce and radish, as well as chemical changes in an Oxisoil due to the addition of tannery waste and hexavalent chromium. Microplots in a greenhouse, which consisted of 60 L plastic pots, received the following treatments: control; lime + NPK; primary tannery sludge + PK; chrome-tanned leather shavings + lime + NPK; finished leather shreds + lime + NPK; Cr6+ + lime + NPK; Cr6+ + lime + cattle manure; lime + cattle manure. The sludge contained 8.5 g kg-1 Cr and was applied at rates of 8.8 t ha-1. The leather shavings contained 17.1 g kg-1 and the shreds, 19.4 g kg-1 Cr. These wastes were applied at rates of 4.4 and 3.8 t ha-1, respectively. The Cr6+ (K2Cr2O7) and the cattle manure rates were 100 mg kg-1 and 20 t ha-1, respectively. Tannery sludge plus PK increased the soil pH (5.1 to 5.8), the soil N (1.26 to 1.51 g kg-1), and the soil Ca (4.1 to 5.9 cmol c dm-3) .Wheat, lettuce and radish yields in this treatment were similar to the ones obtained with lime plus NPK. Chromium concentrations in the soil and crops cultivated with tannery sludge varied from 40.7 to 71.2 and from 0.08 to 2.71 mg kg-1, respectively. These values were considered normal. Additions of chrome-tanned leather shavings and finished leather shreds did not decrease the crop yields or change Cr concentrations in soil or plants. Cr6+ applications caused an intoxication of the plants which provoked a yield drop in wheat and lettuce of 91 and 86 %, respectively, in comparison to lime plus NPK. The toxic effect of Cr6+ decreased when cattle manure was added.
wheat; lettuce; radish; tannery sludge; leather shreds; cattle manure