Degradation of diesel fuel in rhizosphere soil

Little is known regarding the ability of the plant rhizosphere to decompose diesel range organic (DRO) compounds in soil. A growth chamber study was c onducted 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 d iesel fuel, and was treated with: (a) mixed NPK fertilizer; (b) urea; (c) g lucose; 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 decomposit ion of certain long-chain aliphatics in several treatments. DROs decreased most rapidly with the NPK fertilizer, regardless of plant cover. DRO concen trations were consistently lower under legumes compared to the other crop t reatments, regardless of fertilizer treatment. The glucose treatment had lo west DRO reductions, presumably due to preferential utilization of the gluc ose 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.