Effects of tannery and coal mining residues on chemical and biological soil properties and on corn and soybean yields

Tannery and coal residues are potential pollution sources in numerous regions of Brazil, mainly in the Rio Grande do Sul and Santa Catarina States. In order to evaluate the effects of tannery residue and coal mining refuse on soil properties and cultivated plants, a field experiment was carried out in 1996/97 at the UFRGS Experimental Station, in the Eldorado do Sul county, State of Rio Grande do Sul, Brazil. Corn (Zea mays L.) and soybean (Glycine max L. Merrill) were cultivated on 70 m(2) plots of a Paleudult Soil. Tannery sludge additions at rates of 21.3 and 42.5 t ha(-1) with mineral phosphate and potassium fertilization were compared to mineral fertilization (NPK) with liming and a control treatment. Moreover, treatments with (a) coal mining residue (106 t ha(-1)) and mineral fertilization; (b) coal mining residue (106 t ha(-1)) with tannery sludge (21.3 t ha(-1))plus mineral phosphate and potassium fertilization; (c) leather shavings (29 t ha(-1)) with mineral fertilization (NPK), and (d) and a combination of Cr-2(SO4)(3) (125 kg ha(-1) Cr) and 21.3 t ha(-1) tannery sludge with mineral phosphate and potassium fertilization were studied. Chemical and biological soil alterations were evaluated, as well as the effect of residue application on the plant yields and heavy metal uptake. Tannery sludge increased the soil pH, exchangeable Ca, and total Cr contents, while no alterations of the Cu, Cd, Pb, and Ni soil contents were observed. Microbial activity, evaluated by the CO2 production, was stimulated by the residue application, but bacteria, fungi and actinomycete populations were not affected. Tannery sludge applications had a similar influence on soybean and corn grain yields as nitrogen fertilizers. Crop yields were not affected by the addition of leather shavings, while coal mining residue increased the corn grain yield.