Effect of some pesticides on certain micro-organisms, contributing to soil fertility.

A pot experiment was run for studying the effect of Temik (insecticide and nematocide), Orthocide (fungicide), and Treflan (herbicide) on certain desirable soil micro-organisms. Total counts of bacteria, actinomycetes or fungi were mostly lower in the treated than in the untreated soil. Aerobic cellulose-decomposers were either stimulated or depressed. Despite the temporarily slight stimulation, observed in some instances at the initial periods, the effect of the pesticides on counts of Azotobacter, N-fixing clostridia, and ammonifiers was afterwards depressed. The period of retardation or stimulation differed according to type of pesticide and type of micro-organisms under study. However, the autotrophic nitrifying bacteria, especially ammonium-oxidizers, seemed to be more sensitive and their counts in treated soil were sharply depressed.