Effect of two commonly used herbicides on soil microflora at two different concentrations

The effect of two commonly used herbicides (atrazine and atrazine + metolachlor) on non-target soil microflora was investigated over a period of 8 weeks. One kilogram soil samples each from maize farm were treated with the herbicides separately at company recommended and one and half (X1.5) recommended rates. Effects of the herbicides on soil pH and percentage organic matter were also investigated. Significant changes in soil pH and percentage organic matter were observed only in atrazine treated soils (P < 0.05). Herbicide treatments at both recommended and X1.5 recommended rates resulted in decreases in microbial counts. Higher concentrations of herbicides treatments resulted in much lower microbial counts compared to soils treated with recommended herbicide does. Herbicide treatments also resulted in the elimination of some microbial species. Pseudomonas sp. and Bacillus sp. were the most frequently isolated bacteria from herbicide treated soils. While A. niger, A. Flavus, Penicillium sp andTrichoderma sp were the most frequently isolated fungi from herbicide treated soils