Behaviour of herbicides in non-cultivated soils

Contamination of ground water by pesticides is not only caused by their application to agricultural land but also by their use on non-cultivated areas. Therefore the mobility of the herbicides simazine, methabenzthiazuron and diuron was investigated in soils under different types of land use (cultivated field, meadow, gravel track). Undisturbed lysimeters (20 cm x 40 cm) were taken from selected natural plots. After application of the herbicides according to common practice, the lysimeters were incubated under outdoor conditions and disassembled after 20, 50, 100 and 150 days. The soil layers were analyzed for the active ingredients and the disappearence time (DTsub50) of each substance was determined. The results obtained with the soil cores taken from the field and meadow were in good agreement with the Ksuboc values of the active ingredients. Methabenzthiazuron and diuron had the highest degradation rate in the soil from the gravel track due to their higher availability for soil mic roorganisms. The disappearance of simazine was faster in the soil of the meadow than in the other soil types. A leaching of the active ingredients into deeper soil layers occurred already after the first rain events. At the end of the study the total amount of the applied substances in the leachate ranged from 1 percent to 6 percent.