Knowledge about the effects on the ionic balance in the soil solution is important, particularly with respect to residues rich in nitrogen applied with complementary fertilizers because nitrate can reach underground waters. The objective of this study was to verify leaching of nitrate and some associated cations in a soil that received sewage sludge and increasing doses of K2O. The study was carried out in a greenhouse of the Federal University of Paraná, in the Sector of Agrarian Sciences in the municipality of Curitiba, during 2002. Fifteen columns of PVC, (60 cm height, 15 cm diameter) were used, filled with soil previously treated with sewage sludge and cultivated with corn during 2001. The pH and the concentrations of NO3-, K+, Ca2+, Mg2+ e Al3+ in the leachate solutions were determined. In four leachings performed, an increase of pH and of the concentrations of K+ and a reduction of Al3+ in the leachate was verified with the increasing doses of K2O, white no increase in leached nitrate, was observed. All collected solutions presented nitrate and aluminum values superior to the maximum permitted levels, 10 and 0.1 mg L-1 respectively.
nitrogen; underground water; contamination
