Biofiltration of residual fertilizer nitrate and atrazine by Rhizobium meliloti in saturated and unsaturated sterile soil columns

This study was undertaken to investigate whether microbial bioaugmentation of subsurface soil with subsurface irrigation could be used as a biofiltrat ion/biocontrol technology for agricultural pollutants. Nine Plexiglas colum ns, 458 mm long x 139 mm in diameter, were packed with a sterilized sandy l oam soil. Subsurface irrigation, through a controlled water table managemen t system, was used to deliver bacteria, Rhizobium meliloti A-025, to the so il and to maintain aerobic (unsaturated) or anaerobic (saturated) condition s in the columns. Nitrate and atrazine, a fertilizer and a corn herbicide, were applied to the soil surface, and leaching was affected by simulated ra infall events. The soil and drainage waters were analyzed for nitrate and a trazine residues after each rainfall simulation throughout the experimental period during which the soil was kept saturated for a total of 80 days and unsaturated for a total of 70 days. The monitoring of transport and surviv al of the implanted bacterial strain (A-025) showed that subsurface irrigat ion was successful in introducing and transporting the bacteria throughout the soil columns. During the saturated period, significantly more (95% prob ability) nitrate-N leached into the drainage waters from the control column s than from the bioaugmented columns; the increase being 450% or more for t he abiotic control columns. The amount of atrazine that leached into the dr ainage waters during the unsaturated period was also significantly more fro m control columns as opposed to bioaugmented columns, with the increase bei ng 262%.