An experiment was conducted in field for three years to assess the sustainability of aquatic plants Leersia hexandra, Cyperus articulatus, and Eleocharis palustris for use in the removal of total hydrocarbons of weathered oil in four areas contaminated with 60916-119373 mg/kg of hydrocarbons. The variables evaluated were coverage of plant, dry matter, density of plant growth-promoting rhizobacteria, and the removal of total weathered oil. The variables showed statistical differences (p = 0.05) due to the effects of time and the amount of oil in the soil. The three aquatic plants survived on the farm during the 36-month evaluation. The grass L. hexandra yielded the greatest coverage of plant but was inhibited by the toxicity of the oil, which, in contrast, stimulated the coverage of C. articulatus. The rhizosphere of L. hexandra in control soil was more densely colonized by N-fixing bacteria, while the density of phosphate and potassium solubilizing rhizobacteria was stimulated by exposure to oil. C. articulatus coverage showed positive relationship with the removal of weathered oil; positive effect between rhizosphere and L. hexandra grass coverage was also identified. These results contributed to the removal of weathered oil in Gleysols flooded and affected by chronic discharges of crude oil.
In this study were examined chemical, microbiological, and enzymatic changes at different depths of the soil and rhizosphere, produced by the burning of a commercial sugarcane crop in tropical areas of México. Samples of silty loamy soil and rhizosphere were collected at three times in the sugarcane production cycle: before burning (BB), after first burning (AFB), and after second burnings (ASB), with a general interval of 15 days between the first and the third collection date. Soil organic matter (SOM), soil organic carbon (SOC), total nitrogen (Nt), phosphorus available (Pav), pH, and the C/N ratio were determined in soil and rhizosphere, as well as the enzymatic activities of phosphatase and urease. Furthermore, microbial respiration, microbial biomass, and nitrogen-fixing bacteria (NFB) and phosphate solubilizing bacteria (PSB) densities were monitored during 84 days. The Pav and the pH increased significantly in soil samples affected by the second burning of the stubbles, but SOM, SOC, Nt, the C/N ratio, phosphatase, and urease activities decreased as a result of the first and second burnings. This decrease was more pronounced in non-rhizospheric soil. The densities of NFB and PSB increased with the burning, as well as microbial respiration. All the variables evaluated recorded higher values in the soil surface layer.
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