Degradation of Diesel Fuel in Rhizosphere Soil

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Abstract
Little is known regarding the ability of the plant rhizosphere to decompose diesel range organic (DRO) compounds in soil. A growth chamber study was conducted to assess the decomposition of DROs in soil as affected by grasses and legumes. A sandy loam soil was contaminated with 2% (w/w) commercial diesel fuel, and was treated with: (a) mixed NPK fertilizer; (b) urea; (c) glucose; and (d) control (i.e., no additives). Soil was seeded with either a grass mix (Poa, Phleum, Agrostis ), a legume mix (Pisum sativum, Trifolium pratense); or no vegetation; and incubated. Over 150 days, approximately 10.6% of DROs was lost by volatilization. There was a trend toward decomposition of certain long-chain aliphatics in several treatments. DROs decreased most rapidly with the NPK fertilizer, regardless of plant cover. DRO concentrations were consistently lower under legumes compared to the other crop treatments, regardless of fertilizer treatment. The glucose treatment had lowest DRO reductions, presumably due to preferential utilization of the glucose over the aliphatics by micro-organisms. There was no detectable uptake of DROs by either grasses or legumes. Microbial counts increased under both grasses and legumes, but were not significantly (p < 0.05) different from counts in unvegetated soils.