Crude Oil Contamination Effect on The Rhizosphere Soil Properties of Zea mays L. and Vigna unguiculata (L.) Walp.

Crude oil contamination poses a significant threat to soil ecosystems, impacting agricultural productivity and crop growth. This study investigated the effects of crude oil contamination on the rhizosphere soil properties of maize (Zea mays) and cowpea (Vigna unguiculata), two economically important crops, grown in a potted sandy loam soil. Through a series of controlled experiments which were simply arranged in a completely randomised design with four replicates, and four levels of crude oil contamination (0%, 0.5%, 2% and 5% v/w), with each replication containing eight treatments. The control samples were not contaminated. The presence of crude oil in the rhizosphere soil led to significant altercations in microbial diversity and activity, potentially affecting nutrient cycling and overall soil health. These microbial organisms were isolated at ten days interval, which include Nitrosomonas, Nitrobacter, Rhizobium, Azotobacter, Bacillus, Pseudomonas, Aspergillus, Penicillum, Fusarium, Clostridium, Micrococcus, Enterococcus and Arthrobacter. It was also observed that Bacillus spp, Pseudomonas spp, Micrococcus spp, Clostridium spp persisted in the soil after crude oil contamination. Hence, they have potential for degrading petroleum products. Also, the population of petroleum degrading bacteria among the two crops were significantly increased, which ranges from 2.00 to 9.40 x 108 Cfu/g in maize, while 0.50 to 4.90 x 108 Cfu/g in cowpea. As the crude oil contamination rates increases, the growth of nitrifying bacteria, nitrogen fixing bacteria, and fungi were significantly affected in both soil grown with maize and cowpea crop. The results demonstrated a substantial and significant decline in soil pH, nutrient levels (nitrogen, phosphorus and potassium levels), organic matter content, exchangeable bases and acids in the crude oil-contaminated rhizosphere soil compared to uncontaminated soil. Additionally, increased levels of heavy metals were observed in the contaminated soil, indicating a potential toxic impact on crop growth and soil microbial communities. Overall, this study underscored the detrimental effects of crude oil contamination on the rhizosphere soil properties of maize and cowpea, emphasizing the importance of remediation strategies and sustainable agricultural practices to mitigate the environmental consequences of oil pollution on crop production and soil health. Further research is highly needed to explore long-term impacts and develop innovative solutions to address the challenges posed by crude oil contamination in agricultural systems. Key words: Crude oil contamination; Rhizosphere Soil; Soil Properties; Maize; Cowpea; Microbial diversity