Impact of Poultry Manure Amendment on the Microbial Load of Crude Oil-Contaminated Soil.

Crude oil contamination is a major environmental challenge that adversely affects soil quality, agricultural productivity, and ecosystem functioning, particularly in oil-producing regions such as the Niger Delta, Nigeria. One of the most significant consequences of petroleum pollution is the reduction in soil microbial populations responsible for nutrient cycling and hydrocarbon degradation. This study evaluated the effect of poultry manure amendment on the microbial load of crude oil-contaminated soil under screenhouse conditions. A Randomized Complete Block Design (RCBD) comprising five treatments was adopted, consisting of crude oil-contaminated soil amended with 200 g, 300 g, 400 g, and 500 g of poultry manure, alongside an untreated contaminated control. Total heterotrophic bacteria and total fungi were enumerated using standard microbiological procedures. The results showed that poultry manure significantly enhanced microbial populations compared with the untreated control. The highest total heterotrophic bacterial count (4.28 × 10⁵ CFU g⁻¹) and fungal count (4.8 × 10⁴ CFU g⁻¹) were observed in soil amended with 500 g poultry manure, while the untreated control recorded the lowest microbial counts. The increase in microbial populations following poultry manure application suggests that organic amendment provided nutrients and improved soil conditions required for microbial proliferation and hydrocarbon degradation. The findings indicate that poultry manure is an effective, environmentally friendly, and sustainable organic amendment for stimulating indigenous microorganisms and enhancing the biological remediation of crude oil-contaminated soils. Keywords: Crude oil contamination, poultry manure, microbial load, bioremediation, hydrocarbon degradation, soil restoration.