To investigate the degradation and persistence of 2,4-D and Atrazin in soil under climatic and soil conditions, during 2002, 2003 field trials were carried out with ifferent amounts of these herbicides at various locations in Nazar Abad (Karaj), Kamiyaran and Dinavar (Kermanshah). Using multi-stage sampling, dispersion and
disintegration processes were determined. At application rates of 2 kg/ha, both herbicides were not leached. beyond 10-15cm. At rate of 6 kg/ha, these herbicides could significantly be detected in the 15-20 cm soil layer and herbicide residues were still present in the soil after one year. Within each degradation curve, different velocities of breakdown occured. At the beginning breakdown was slow, then rapid herbicide degradation was found followed by a slower phase at the end.
The duration of dispersion was completely different in various soils and conditions.