The effect of two herbicides, - atrazine and paraquat on soil bacterial population, soil pH and percentage
moisture content was assessed over a period of eight weeks. Soil samples from uncultivated, open field were
treated with herbicides at recommended rates and half (0.5x) recommended rates. The soil pH was affected
while the differences in percentage moisture content of the treated soils depended on factors other than the
treatment. Each collection point was sampled at two depths, 10 and 20 cm. Bacterial populations decreased
upon treatment with herbicides at both concentrations when compared with the control (untreated soil).
Concentrations of herbicide treatments at recommended rates resulted in much lower bacterial count and
diversity compared to soils treated with half the recommended dose. The bacterial population for all treatments
dropped at the 4th week of post treatment, but increased progressively at the 6th and 8th week. Herbicide
treatments also resulted in the suppression of some bacterial species, e.g. Proteus sp, and Actinomycetes.
Bacillus sp. and Pseudomonas sp. were the most frequently isolated bacteria from herbicide treated soils.
Thus, the microorganisms which were sensitive to herbicide application, therefore, could serve as a reliable
indicator of the biological value of soils while the resistant ones could be further studied for bioremediation
purpose.