EN
The experiment was carried out in outdoor lysimeters, filled with highly organic soil. The soil surface was divided in two sub-fields and then treated with the commercial product Dual 960 EC enriched with 14C – UL – metolachlor, at a dose of 1.8 l/ha. After the pesticide treatment the soil surface was sprinkled four times either with water or with biohumus solution. The dissipation of metolachlor in the 0–15 cm of soil profile was investigated during 11 weeks. Soil samples collected from the levels of 0–5, 5–10 and 10–15 cm were analyzed on extractable and bound 14C residues. Sprinkling with water caused a vertical movement of metolachlor in the soil. After 11 weeks 92% of applied 14C was found. Under the organic fertilization the dissipation of herbicide within soil profile was limited, mainly due to binding of its residues at top-layer of 0–5 cm. In this case, in soil profile of 0–15 cm almost the whole amount of applied 14C was found after 11 weeks. These results showed that biohumus was an effective agent for protecting groundwater from contamination by pesticides. On the other hand, they suggest that the binding of xenobiotics is a factor which limits the removing of potentially harmful substances from the soil.