Asian Soil Research Journal

Aim: This study evaluated the impact of pesticide use on soil bacterial community structure, abundance and diversity. Pesticide treated (PT) and untreated (UT) soils were obtained from a farmland at Onuebum Community, Bayelsa State, Nigeria. The UT soil served as the control.

Place and Duration of Study: Department of Microbiology Laboratory, Federal University Otuoke, Bayelsa State, Nigeria, between May 2025 and June 2025.

Methodology: The soils were analyzed for pesticide residues and phospholipid fatty acids (PLFA) using Gas Chromatography-Mass Spectrometry (GC-MS). Isolation, enumeration and identification of bacterial species were done using standard microbiological techniques.

Results: GC-MS revealed that PT soil had four organochlorine residues; Alpha-BHC (11.55 µg/kg), Aldrin (12.93 µg/kg), Heptachlor epoxide (1.05 µg/kg) and Gamma-chlordane (16.39 µg/kg) above Maximum Residue Limits (MRL) (7.4, 5, 0.6 and 4 µg/kg) respectively. However organophosphate residues in the soils were all below MRL (0.05 µg/kg). The UT soil had one organochlorine residue; Heptachlor epoxide (4.08 µg/kg) above MRL (0.6 µg/kg), while others were below MRL. The PT soil had one PLFA; palmitic acid (biomarker for General Bacteria) out of the compounds detected, while the UT soil had 18 PLFAs (biomarkers for General Bacteria, Fungi, Gram negative and Gram positive bacteria). The mean total csulturable heterotrophic bacterial counts (TCHBC) recorded for PT and UT were 7.1 × 10⁴ and 2.3 × 10⁴ CFU/g respectively. A total of 9 and 6 bacterial isolates were recovered from PT and UT soils respectively. The identified isolates from UT soil were (Bacillus pumilus, Burkholderia cepacia, Chromobacterium sp., Bacillus spp., Serratia sp., Streptococcus sp.) and PT soil (Bacillus thuringiensis, Lysinbacillus xylanilyticus, Klebsiella quasipneumoniae, Enterobacter mori, Rossellomorea marisflavi, Priestia megaterium, Chryseobacterium gleum, Lysinibacillus sphaericus).

Conclusion: Findings from this study reveal a shift in the microbial community structure from a more diverse structure observed in UT soil to a less diverse structure observed in PT soil, selecting for mostly Bacillus species in (PT soil) known for their resilience under environmental stress. Therefore, integrated pest management and pesticide stewardship are recommended to reduce the negative impact of pesticides on agricultural soils.