Quantitative effects of some pesticides on certain physiological groups of micro-organisms in soil.

Quantitative effects of temik (insecticide and nematocide), orthocide (fungicide), or treflan (herbicide), added to soil at field rate application, on counts of certain desirable soil microorganisms were studied. In the presence of any of the pesticides, counts of aerobic cellulose-decomposers were either stimulated or depressed. Despite the temporarily slight stimulation, observed in some instances of the initial periods, the effect of any pesticide on counts of Azotobacter, N-fixing clostridia, and ammonifiers was subsequently depressive. The period of retardation or stimulation differed according to the chemical composition of the pesticides and physiological properties of micro-organisms. However, the autotrophic nitrifying bacteria, especially ammonium-oxidizers, seemed to be more sensitive and their counts in treated in treated soil were sharply depressed.