Impact of pesticide applications on the populations of some soil microflora and fauna in the vegetable growing area of Akomadan, Ashanti Region of Ghana.

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A questionnaire survey was carried out among randomly selected farmers, herbalists and hunters to obtain background information on the status o some plants and animal species of community interest in Akomadan, an intensive tomato producing area in the Ashanti region of Ghana. The study revealed that some species of plants and wild animals had disappeared or become rare. In addition, the effect of the continuous and indiscriminate use of pesticides on the population sizes of some indigenous microflora (bacteria, fungi and actinomycetes) and fauna (nematodes and earthworms) was investigated in fields where conventionally large quantities of pesticides are used annually. Soils were obtained from (i) fields currently under tomato cropping with pesticide management (ii) fields under different fallow periods (i.e. 1, 2 and 3 years) with histories of pesticide applications. Control soils were obtained from fields with no known history of pesticide applications. Populations of total aerobic bacteria, fungi and actinomycetes in the control fields were consistently higher than in fields with histories of pesticide applications. Six bacterial isolates, five fungi and two actinornycetes were identified from the control area. Reductions in the number of species of microbes were observed in soils from fields with histories of pesticide applications as compared to the control soils. Nematode and earthworm populations in the control soils were also higher than those in soils currently under tomato cropping with pesticide management. Similarly, populations of nematodes and earthworms in soils from fields under fallow were higher than those from fields currently under tomato cropping. Generally, observations in this investigation indicated that some species of plants and wild animals of community interest in Akomadan have become rare or disappeared. The study also revealed the negative environmental impacts of the long term pesticide use on the populations of microbes, nematodes and earthworms in the soil. However populations were able to recover after a break in pesticide applications. To ensure the maintenance of biodiversity, policies related to biodiversity conservation, food security, agricultural research and forestry management should be strengthened by the government. In the case of the effect of pesticide applications on soil organisms, long term investigations need to be conducted in order to obtain statistically significant results due to seasonal variability in microbiological and biochemical soil processes. Further, in the design of pest management strategies, the potential for the beneficial manipulations of soil floral and faunal communities to improve soil fertility should be considered.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, in partial fulfilment of the requirements for the award of in Environmental Science, 2001