Impact of Pesticides on Microbial Diversity and Enzymes in Soil

Abstract

Introduction: The presence of pesticides in soils could result in alterations in microbial activities (enzyme activities, microbial populations), soil physical and chemical properties. Research gap/Challenges: Insufficient literatures on extensive monitoring of soil quality through enzyme activity, during pesticides application. Existing literatures concerning analysis of effect of pesticide application on soil enzyme activity are not comprehensive with respect to number of soil enzymes analysed. Aim/Objective: The study was conducted to investigate the effect of carbofuran and paraquat on soil biochemical characteristics on certain soils in the Niger Delta region of Nigeria. Methodology: These pesticides were applied at recommended doses, their effects on soil organic carbon, enzymes activity and microbial populations were assessed using standard methods. The enzymes monitored were amylase, invertase, protease, urease, phosphatase and dehydrogenase. Microbial counts were carried out for total heterotrophic bacteria, fungi, actinomycetes, nitrifying bacteria and phosphate solubilizers using the spread plate method. Results: There were variations in the different enzyme activities in carbofuran – and paraquat - treated soil during this research. Dehydrogenase activity increased in treated soils. Also, urease activity was lower compared to other enzyme activities. As the study progressed, variations in values of soil organic carbon were observed.  There was a gradual increase in microbial counts and can be traceable to their ability to temporarily mineralize and use the pesticides as carbon and energy source. The soil organic carbon, enzymes and microbial counts values were significantly different at P=0.05. Conclusion: This research revealed that the pesticides cause temporal impact on microbial populations and enzyme activities, associated with the pesticide type at recommended field application rates. A change in numbers, activity and diversity of soil microorganisms may act as indicators of soil fertility and reflect the soil quality.