EFFECTS OF TERBUTHYLAZINE ON SOIL FAUNA AND DECOMPOSITION PROCESSES

Acute lethal and sublethal effects of terbuthylazine and the commercia l herbicide preparation Gardoprim [terbuthylazine is the active ingred ient (a.i.)] on soil organisms (microbes, oppioid mites, two gamasid m ite species, enchytraeids, and nematodes) were studied. In the humus s oil terbuthylazine had no toxic effects on soil animals tested. Howeve r, the herbicide preparation had acute toxic effects on enchytraeids [ no-observed-effect level (NOEL) 1.0 g a.i./m(2)] and both gamasid mite s (NOEL 2.4 and 5.0 g a.i./m(2)). According to filter paper test, the LC(50) value for oppioid mites was 14.5 g a.i./m(2). In the humus soil the commercial preparation caused no dose-related mortality in Oppioi dea. The preparation was more toxic to gamasid mites when the herbicid e was applied on the soil surface compared to the treatment in which t he chemical was mixed into the humus. Application method of the chemic al did not affect the mortality of enchytraeids. In the multispecies e xperiment, the number of nematodes was higher in the highest concentra tion of the commercial preparation (50 g a.i./m(2)) compared to the lo west concentration (1 g a.i./m(2)) and the clean soil. The amount of N H4+-N in the humus tended to increase with increasing herbicide concen tration. The herbicide did not affect soil respiration, microbial biom ass, or water content of the humus, These results indicated that herbi cides can have direct effects on soil fauna, Due to species-specific f oraging strategies or different exposure routes and rates to animals, effects of herbicides on soil animals varied considerably, Single-spec ies toxicity tests performed in humus soil were more sensitive to the effects of herbicide than ecologically relatively short-term multispec ies test. (C) 1996 Academic Press, Inc.