Submitted to: World Congress of Soil Science
Publication Type: Abstract Only
Publication Acceptance Date: February 21, 2006
Publication Date: July 9, 2006
Citation: Guber, A.K., Pachepsky, Y.A., Shelton, D.R. 2006. Attachment of manure-borne Escherichia coli to soil. 18th World Congress of Soil Science, Philadelphia, PA. July 9-15, 2006. CD-ROM, Paper No. 139-28.
Attachment of bacteria to soil is an important component of the bacteria fate and transport. Escherichia coli is commonly used as an indicator of fecal contamination in the environment. Despite the fact that E. coli are derived exclusively from feces or manure, effect of the presence of manure colloids on bacteria attachment to agricultural soils was never directly studied. The objective of this work was to evaluate the magnitude of the E. coli attachment to soil in presence of manure. Escherichia coli attachment to soil was studied in breakthrough and batch experiments.
Breakthrough column experiments were conducted with undisturbed, 20-cm long columns of Tyler clay soil from the A horizon. A pulse of 4 % filtered bovine manure solution with E. coli was passed through the initially water-saturated columns. The E. coli content and turbidity were measured in the effluent collected from the bottom of the columns. The manure content was calculated in the effluent from the turbidity measurements using the calibration. Columns were cut into 2-cm layers after the experiment to measure viable bacterial concentrations in pore solution and attached to soil. Flow velocity affected E. coli transport and attachment to soil. There was relatively more attachment at slower flow velocity than at higher flow velocity. The E. coli attachment to soil was 18%, 5%, and 9% at flow velocities of 2.3, 8.4, and 9.3 cm day-1, respectively. The higher was the velocity, the more E.coli and manure were released from columns.
We hypothesized that manure affected E. coli attachment to soil and facilitated the E. coli transport. To corroborate this hypothesis, we measured attachment of E. coli to soil in the presence of various amounts of manure. Three soil textures were used for the batch experiment. Samples of the loam soil were taken from the A horizon of Tyler soil. Clay loam and sandy clay loam samples were taken from topsoil in Beltsville, Maryland. Escherichia coli cells were added to the water–manure suspensions containing 0, 2, and 4 % of filtered liquid bovine manure, which subsequently were equilibrated with air-dry sieved soil in different soil-to-suspension ratios. Manure dramatically affected E. coli attachment to soil. Attachment isotherms were closer to linear without manure and were strongly nonlinear in the presence of manure. The maximum E. coli attachment occurred in the absence of manure. Increasing manure content generally resulted in decreased attachment. Similarity was observed between E. coli attachment isotherms measured in the breakthrough and the batch experiments. The decrease in bacteria attachment to soil could be caused by (a) modification of soil mineral surfaces by soluble manure organic and inorganic constituents; (b) competition of dissolved organic matter and bacteria for adsorption sites; (c) modification of bacteria surfaces by the dissolved organic matter.