Effect of Soil Treatment with the Organophosphorus Insecticide Profenfos on the Fungal Flora and Some Microbial Activities

Tests were conducted to determine the effects of Profenfos [(0-(4-bromo-2-chlorophenyl) 0-ethyl S-n-propyl-phosphorothioat] on fungal populations and some activities in soil. Profenfos (at 5.4 micrograms active ingredient/g dry soil), has a significant adverse effect on the count of total fungi after 2, 4 and 6 weeks after treatment. This effect was completely alleviated after longer incubation. Incorporation of this insecticide into the agar medium inhibited the total count of soil fungi at 6.4 and 38.4 micrograms ml-1. Initial activation followed by a decrease in CO2 output occurred in soil treated with 5.4 micrograms a.i./g. The two doses of Profenfos accelerated urease activity for 6 weeks after soil treatment, but inhibited the enzyme activity after longer periods. An inhibitory effect on nitrate reductase activity was observed with some insecticide treatments in the early stages of incubation followed by an activation in certain cases.