EFFECTS OF CRUDE OIL ON THE GROWTH OF Brachiaria mutica AND Leucaena leucocephala AND ON SOIL AND PLANT MACRONUTRIENTS

Abstract

This study assessed the effect of 150, 50000 and 78000 mg kg-1 of fresh crude oil (FO) and 78456 mg kg-1 of weathered crude oil (WO) on the growth of Brachiaria mutica and Leucaena leucocephala. The variables measured were plant height, dry biomass, nitrogen (N), phosphorus (P) and potassium (K) contents in soil and plant, density of rhizospheric bacteria and fungi, and FO and WO degradation. Statistical differences were found (P ≤ 0.05) in all variables. Leucaena leucocephala was more sensitive to oil toxicity than B. mutica. In L. leucocephala FO caused the death of the plant from the second month, while WO led to a 6-fold reduction in height. The FO had no effect on biomass accumulation of B. mutica but it reduced it in L. leucocephala, whereas WO decreased biomass in both species; N, P and K accumulation decreased in B. mutica in soil with WO and in L. leucocephala in soils with FO and WO. Density of rhizosphere bacteria was inhibited by WO in both species; there were fewer fungi in soil with FO in B. mutica and in soil with WO in L. leucocephala. Degradation of FO and WO was higher in B. mutica rhizosphere soil, so this grass may be an alternative for decontaminating soils polluted with FO and WO.