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Research Journal of Agronomy

Year: 2007  |  Volume: 1  |  Issue: 1  |  Page No.: 33 - 37

Biological Effects of Four Fungicides on Soil Microbial Population

O.A. Ojo, T.A. Adebayo and O.A. Olaniran


The biological response of bacteria, actinomycetes, fungi and protozoan to four fungicides (Phenyl mercuric acetate, pentachloro-nitrobenzene, benomyl and captan) was investigated in a garden soil treated with three different rates of these fungicides. The microbial populations were estimated at different days after treatment using the standard dilution plate-count technique. Phenyl mercuric acetate completely inhibited the soil bacteria and fungi at all rates of application up till 33 Days After Treatment (DAT), after which recolonization of the soil occurred. The significantly (p 0.05) highest bacteria population of 22.11 x10 cfu g-1 and 16.03x10 cfu g-1 of actinomycetes population in soil was observed in the soil samples treated with benomyl at the application rate of 225.0 ìg g-1 and 63DAT when compared with that of untreated soil sample. Pentachloro Nitrobenzene (PCNB) gave significantly lowest (p 0.05) population of actinomycetes (0.03x10 cfu g-1) and protozoan (0.0x10 cfu g-1) compared to all other treatments throughout the period of study. The actinomycetes population in the captan and ceresan treated soils sample increases with days after treatment. In general, fungi and protozoa were more susceptible to fungicides than bacteria and actinomycetes. Phenyl mercuric acetate and pentachloro-nitrobenzene were more toxic particularly to soil, micro organisms, compared to benomyl and captan. The significant effects of fungicides on soil microbial population is here in discussed.