Biodegradation of Petroleum Hydrocarbons in a Tropical Ultisol Using Legume Plants and Organic Manure

Global emphasis on food security and soil health should consider rehabilitation of degraded lands, especially where oil contamination limits the use of such lands. Three legume plants (Gliricidia sepium, Leucaena leucocephala and Calapoconium caerulean) alone or along with 0.5% (w/w) (equivalent of 10 tons ha-1) poultry manure, were used to treat the soil, in which the oil residuals were monitored for three years. Results showed that significantly high levels of residual total petroleum hydrocarbon content (RTPHs) persisted in the non-amended soil after 36 months. At 3 months, 43% of RTPHs was removed by Gliricidia sepium and Leucaena luecocephala along with poultry manure. Net loss of RTPHs after 12 months was 69% for Gliricidia sepium and Leucaena luecocephala combined with poultry manure and only 38% for A5, explaining that, degradation of petroleum hydrocarbon by indigenous soil micro-organisms was very low. At 18 months when additional load of oil was applied, the degradation rate increased from 71.7 mg kg-1 day-1 to 142 mg kg day-1 within 6 months for all the legume plants along with poultry manure. This explained increased in number of hydrocarbon-degrading micro-organisms due to increase in oil load. The oil inhibited germination and yield of maize crop completely. Treatments with legume plant along with poultry manure significantly (p < 0.05) increased both germination and yield of maize crop. The effects of legume plants combined with poultry manure were the better treatment than legume or poultry manure alone in improving the soil properties for growth and performance of maize crop.