Influence of fertilizer levels on phytoremediation of crude oil-contaminated soils with the tropical pasture grass Brachiaria brizantha (hochst. ex a. rich.) stapf.

Determination of fertilizer levels in phytoremediation of petroleum hydrocarbons is a complex issue, since nutrient demands of the plant and of degrading microorganisms in the rhizosphere have to be considered In the present work, three fertilizer levels were tested in a greenhouse experiment with the aim of optimizing growth of the tropical pasture grass Brachiaria brizantha and enhance microbial degradation of heavy crude oil in soil Fertilizer was applied twice in a concentration of 200, 300, and 400 mg each of N, P, and K per kg soil before and after the first sampling (14 wk). The medium fertilizer concentration resulted in best root growth and highest absolute oil dissipation (18.4%) after 22 wk The highest concentration produced best shoot growth and highest relative oil dissipation after 14 wk (10.5% less than unplanted control). In general, degradation of total oil and grease was higher in planted than in unplanted soil, but differences diminished toward the end of the experiment. Next to fertiizer quantity, its composition is an important factor to be further studied, including the form of available nitrogen (N-NO3- vs. N-NH4+). Field trials are considered indispensable for further phytoremediation studies, since greenhouse experiments produce particular water and nutrient conditions.