Interaction between herbicides and soil microorganisms.

Abstract

Herbicides have been selected for their ability to act in a phytotoxic manner. Whilst considerable research effort has been conducted into their spectrum of activity on plants and animals (including man), little attention has been paid to the interaction between these compounds and the soil microorganisms. Yet it is largely through the activity of this flora that the fertility of the soil is maintained (Burgess and Raw 1967). The realization that some interaction could exist did not become apparent until studies on the persistence of these herbicides in the soil showed that whilst some compounds survived for a considerable length of time, others were degraded (Audus 1964, Kearney and Kaufman 1969). Parallel studies on insecticides showed that many of these could also persist for long times in the soil (Way and Scopes 1968). In this work, heavy treatments of phorate 1 and menazon were found to kill a large fraction of the soil population before degradation took place. The rate of degradation was found to vary enormously from pesticide to pesticide. Some of the organochlorine pesticides have been found to take years to disappear from the soil. There is some evidence that microorganisms may play a role by a very slow degradation of such compounds. Dieldrin, for example, can be partially hydrolysed by the bacterium, Aerobacter aerogenes (Wedemeyer 1968).