Microbial populations and enzyme activities in soil treated with pesticides

The effect of soil treatment with brominal (a herbicide) and the insecticide selecron (the equivalent field rates and five-fold) on population counts of bacteria, actinomycetes and celluloytic fungi in soil was tested throughout 10 weeks incubation at 28 degreesC. Also, tested their effect on four soil enzymes: cellulase, acid phosphatase, alkaline phosphatase and arylsulphatase. Bacterial and actinomycetes populations in soil treated with the two pesticides were promoted at field application rates and inhibited at higher levels. The two pesticides significantly decreased the total number of cellulolytic fungi and most fungal species after most incubation periods either by one or the two used levels but the effect of selecron was more pronounced. Cellulase activity in soil treated with brominal and selecron was inhibited after most incubation periods. The effect of soil treatment with the two pesticides on acid phosphatase was promotive at field application rates after some incubation periods but the enzyme activity was delayed at the higher application doses. Alkaline phosphatase activity in treated soil was accelerated with both pesticides even at the higher application rates, suggesting a direct role of alkaline soil pH in increasing resistance of alkaline phosphatase to pesticides. The effect of soil treatment with pesticides on arylsulphatase activity fluctuated between promotion and inhibition, but inhibition was predominant.