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either to a direct effect of the herbicide on the microorganisms or an effect on the relationships of the bacteria, actinomycetes, and fungi. The lower fungal population in the trifluralin-treated plot may be the result of a combination of factors. It is possible that actinomycetes may increase in numbers because of their ability to metabolize the chemical. This could result in severe competition for nutrients, in which the fungi are unsuccessful. It has been demonstrated that actinomycetes and bacteria often produce fungistatic substances which may reduce the observed numbers of fungi over a long period of time (3, 7, 9). Another factor involved could be direct inhibition of fungal growth by trifluralin. 2,4-D appeared to exhibit an inhibitory effect on the toFrom the data presented, it is evident that the microfloral populations in herbicide-treated soil have been altered. A change in the normal soil microfloral balance may be either beneficial or harmful to soil fertility. Thus, it seems that a moretal bacterial population.critical evaluation of the effects of soil-applied herbicides on microbial populations is needed.