Impact of Crude Oil on Soil Nitrogen Dynamics and Uptake by Legumes Grown in Wetland Ultisol of the Niger Delta, Nigeria

The effects of crude oil on soil nitrogendynamics and cycling in plant-soil ecosystems and its effect on the growth oflegumes (Calopogonium mucunoides, Centrosema pubescens and Puerariaphaseolodes) grown in wetland ultisols were investigated. The testplants species were grown on wetland soil simulated with 0.35, 10.8, 20.5, and50 g.kg-1levels of crude oil contamination. The resultsshowed time and species dependent variation in mineral N content of the treatedsoils. The variation is indicative of significant interaction between thehydrocarbon content and plant species. Variations in microbial N and microbialC were similar and correlation between the microbial N and the total C (Organicmatter (C) + hydrocarbon content (C)) in soil was highly significant (r = 0.96,n = 12, P ≤ 0.01). The presence of hydrocarbon contaminant widens the C:N ratioin soil and leads to more available N being immobilized by soil microorganisms,which reduces available N for plant uptake. This result implies that crude oilcontamination significantly reduces N uptake by plants but increases Naccumulation in soil microbial biomass. The findings show that N dynamics,transformation and cycling in soil are influenced by hydrocarbons and that theinteractions between hydrocarbon content and plant species in contaminated soilare remarkable. The use of plant Centrosema pubescens withpoultry manure or NPK fertilizer for bioremediation is more effective than thatof Calopogonium mucunoides and Puerariaphaseoloides. However, the selective attributes of thevarious treatment approaches adopted here may be exploited for enhancedremediation of contaminated wetlands in the Niger Delta region of Nigeria.