Persistence of captan and its effects on microflora, respiration, and nitrification of a forest nursery soil

Abstract

Addition of captan, n-(trichloromethylthio) 4-cyclohexene-1,2-dicarboximide (active ingredient, 62.5, 125, and 250 ppm/acre) to fresh soil in the laboratory affected the soil microflora and some of their activities. Captan showed extremely low persistence in a forest nursery soil. It was almost fully degraded in 1 week when applied at or below 250 ppm. Captan killed the population of two pathogenic fungi (Rhizoctonia and Pythium species) and encouraged the growth of three saprophytic fungi (Penicillium, Trichoderma, and Fusarium species). After an initial decrease, the population of actinomycetes gradually increased. Captan increased the population of bacteria by the 7th day; however, by the 35th day the population had dropped to that of the control soil.Captan also affected soil respiration. Initial depressions of CO2 production were directly proportional to the concentration of captan in the soil. After initial inhibition, the rate of soil respiration was stimulated because of the use of decomposition products of captan by microorganisms. Nitrification was impaired for 2 to 3 weeks, depending on the captan concentration.