INFLUENCE OF NATURAL AND ARTIFICIAL HUMIC ACIDS ON DECREASE OF Zn AND Cd TOXICITY FOR PEA PLANTS (Pisum sativum L.)

Summary. This article presents a study on the effect of natural and artificial humic acids on zinc and cadmium toxicity for pea plants (Pisum sativum L.). The research was carried out in water cul-tures on the modified Knopp substrate. Toxic quantities of Zn and Cd were added to the substrate in the form of soluble nitrogen salts. Two natural humic acids were prepared from Luvisol and de-graded chernozems. Artificial humic acids came from Aldrich company. Different influence of both natural and artificial humic acids point out to three mechanisms: (i) difference of cation ex-change capacity and amounts of carboxilic and phenolic groups of all amendments; (ii) chemical properties of zinc and cadmium ions; (iii) ratio between amount of three types of humic acids and metal contents. Humic acids from Aldrich company were a factor determining zinc and cadmium activity for pea plants. Humic acids from degraded chernozem caused a decrease of cadmium activity of investigated plans. Key words: humic acids, zinc and cadmium toxicity, pea plant