EFFECT OF A FUNGICIDE, CHLOROTHALONIL, ON CELLULOSE DECOMPOSING PROCESS IN SOIL

The effect of chlorothalonil (Daconil(R) 1000) application on cellulos e decomposing process in soil, and the impact.and duration of the effe ct were estimated in laboratory experiments at 23-degrees-C and 13-deg rees-C under upland conditions. In the soil just after the application , the pesticide caused the retardation of cellulose decomposition and the shifts in the balance of fungal flora on the cellulose sheets at d oses above 75 mug a.i./g-soil at 25-degrees-C and at doses above 15 mu g a.i./g-soil (recommended rate of the pesticide for drenching) at 13- degrees-C. In the soil after 10 weeks of the application, no retardati on in cellulose decomposition and incomplete recovery of the fungal fl ora were observed at doses of 75 mug a.i./g-soil at 25-degrees-C. Rela tive dominance and frequency of a fungal species, Rhizoctonia solani, on the cellulose sheets at 13-degrees-C were high in the control soil but low in applied soil. The retardative effects of the chlorothalonil application on cellulose decomposition in the soils at low temperatur e seem to be attributable to reduction in the dominance of R. solani o n the cellulose sheets. Since the species is one of the target pathoge n for the drenching of chlorothalonil, the retardative effect on cellu lose decomposition should be defined as a side-effect in respect of ph enomenon, whereas, as a objective effect in respect of mechanism. Thes e results represent the importance of research on the structure of mic roflora and consideration on the environmental condition such as tempe rature in assessment on effect of pesticide on soil ecosystem.