EFFECT OF LONG-TERM APPLICATION OF A FUNGICIDE, CHLOROTHALONIL, ON CELLULOSE DECOMPOSITION AND MICROFLORA IN SOIL UNDER UPLAND CONDITIONS

Effects of long-term, repeated application of chlorothalonil on cellul ose decomposition in soil and soil microflora were estimated in field experiments under upland conditions. Chlorothalonil was applied to a p lot twice a year for six years at the rate of 2.25 g a.i./m2 (normal-d osage plot) and 11.25 g a.i./m2 (high-dosage plot). In the normal-dosa ge plot, cellulose decomposition was suppressed only in winter. Such a seasonal variation was also observed in the high-dosage plot with inc omplete recovery in summer. High-dosage, long-term application increas ed the populations of total and gram-negative bacteria and decreased t he population of actinomycetes in the soil. The populations of total a nd Cx-cellulase (1,4-beta-D-glucan 4-glucanohydrolase, EC 3.2.1.4) pro ducing fungi remained unchanged, while the population of fungi which v igorously decomposed filter paper decreased as the application rate, f ungal inoculum potential to decompose crystalline cellulose completely at 25-degrees-C decreased only in the high dosage plot. It was suppos ed that the suppression of cellulose decomposition in the high dosage plot was attributed to the difference in fungal flora in the soil rath er than to the low fungal population level.