EFFECTS OF THE 2, 4-DICHLOROPHENOXYACETIC ACID (2,4-D) HERBICIDE CONTAMINATION ON SOIL MICROBIOLOGY AT THE COMMUNITY LEVEL

Owing to the knowledge that 2, 4-Dichlorophenoxyacetic Acid (2, 4-D) is rapidly degraded by soil microorganisms, little or no research attention has been given to enhancement of its degradation as a form of environmental remediation. A completely randomized design laboratory incubation experiment was carried out to examine the potentials of organic and mineral fertilizers to stimulate microbial activities in soils under the influence of the 2, 4-D herbicide. Soil contaminated with the field rate of 2, 4-D was separately amended with compost and NPK mineral fertilizer, and the treated samples were incubated for 56 days at room temperature. Soil microbiological parameters were measured in dynamics and eco-physiological quotients were computed at the end of the incubation period to determine responses of soil microbes at the community level of the treatments. Application of 2, 4-D either alone or in combination with fertilizer, regardless of type, raised soil respiration and soil microbial biomass. Addition of NPK to the 2, 4-D contaminated soil increased the microbial metabolic quotient (qCO2) while this parameter was reduced when compost was added. Addition of compost improved all the eco-physiological quotients compared to the sole application of 2, 4-D herbicide. It was therefore concluded that the 2, 4-D herbicide at the field recommended rate has the potential to negatively influence the soil microbial community, application of organic fertilizer may help the soil to regain its microbial competence through enhanced degradation engendered by bio-stimulation of native microorganisms.