Persistence of herbicides in forest nursery soils

Abstract

The persistence of the four herbicides atrazine, hexazinone, lenacil and linuron was studied in forest nursery soils. The adsorption capacities of the soils for the chemicals were described by the distribution coefficients kj and k_oc. Due to the low content of organic matter in the soils the k_a‐values were low, in several cases being <1 for hexazinone. Hexazinone also had the lowest k _oc‐value (30) while the other substances had k_oc ‐values within the range 200–400. In some cases hexazinone showed great mobility under field conditions. The formula c=c_o‐kt^1/2 was used to describe the disappearance of the herbicides from the various soils. The rate of degradation of the four herbicides correlated well with the rate of respiration in the same soils in laboratory experiments, and for linuron reasonably well also in field experiments. In the field experiments the herbicides penetrated the top soil layer. In the subsoil the risk of further transport downward to the drainage system or ground water increased, especially for hexazinone. Linuron as well as the fungicides maneb and tolylfluanid suppressed the decomposition rate of hexazinone in laboratory experiments.

Key words:

• herbicide
• atrazine
• hexazinone
• lenacil
• linuron
• forest nursery
• persistence
• adsorption
• mobility