LEVELS OF TOXIC METALS IN THE LEAVES OF MAIZE FERTILIZED WITH TANNING RESIDUE

In this study, were measured levels of the toxic metals Cr, Cd, Ni, and Pb in leaf tissues, as well as the green matter yield of the aerial part of maize plants. The plants were grown in pots with a soil substrate (Oxisol), fertilized with tanning residue, in doses of zero (control), 113.1 mL (36 m3.ha-1), 226.2 mL (72 m3.ha-1), 452.4 mL (144 m3.ha-1), and 904.8 mL (288 m3.ha-1) per pot, with mineral fertilizer only, and with the combination of mineral fertilizer and tanning residue. The treatments were applied in four replications in greenhouse conditions, in the period of August to November 2003, in Santo Antônio de Goiás, Brazil. The tanning residue was added to the soil twenty days before sowing and the mineral fertilizer NPK 4-30-16 + Zn (1.256 g per pot, or 400 kg.ha-1) was added during the sowing of the corn hybrid BR 205. The mean levels of toxic metals Cr, Cd, Ni, and Pb obtained in the leaves fifty days after emergence were below or within acceptable limits for these tissues. The largest levels of Cr (0.147 mg.dm-3) were usually observed in the treatments with the largest doses of the tanning residue. The aerial part green matter of the corn plants increased with increased doses of the residue. The addition of tanning residue to the substrate, in different doses as a source of nutrients for maize, presented promising results. KEY-WORDS: Plant nutrition; toxic metals; industrial residue; green matter.