keywords: Crop production, environmental sustainability, heavy metals, herbicide
Herbicides not only control weeds but also affect soil microorganisms which are responsible for numerous biological processes essential for crop production. The study aimed at determining the effect of herbicide contaminated soils on its physicochemical, microbiological and some enzymatic properties. Standard methods were used for soil sampling and analyses. The physicochemical parameters recorded were pH (5.17 – 5.41), electrical conductivity (98.00 – 237.00 uS/cm), particle size (89.21 – 91.11%) and heavy metals with iron being the highest at all contaminated locations (44.10 – 106.65 mg/kg). There was high significant difference in physicochemical parameters at locations A, C and E (P<0.001). The three impact assessment indices revealed the same pattern of heavy metals contamination; Pb2+ > Cr2+ > Fe2+ > Cu2+ > Zn2+ > Mn2+ > Ni2+. Location E had the highest heterotrophic bacterial and fungal counts of 4.19 x 106 and 1.85 x 106 cfu/g, respectively while location A had the least of 2.78 x 106 cfu/g and 1.13 x 106cfu/g for bacterial and fungal respectively. The microorganisms identified were Pseudomonas fluoriscens, Penicillium sp. and Aspergillus niger, 13.64%; Bacillus sp. 11.36%; Staphylococcus aureus, Corynebacterium, Rhizopus and Candida species, 9.09%; Serratia sp. 6.82% and Escherichia coli, 4.55%. Pseudomonas flouriscens produced the highest enzyme, maltase with concentrations of 0.313, 0.407, 0.421 and 0.429 mg/ml at days 2, 4, 6, and 8, respectively closely followed by invertase with 0.363, 0.421 and 0.429 mg/ml at day 4, 6 and 8, respectively. Herbicide application had negative impact on the soil properties studied. This study recommends that maltase, invertase and amylase enzymes produced by Pseudomonas fluoriscens could be employed as biocatalysts for treating herbicide contaminated soils so as to guarantee environmental safety and public health for all.