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Saturated and unsaturated transport of cow manure-borne Escherichia coli through in situ clay loam lysimeters

Mosaddeghi, M.R., Sinegani, A.A. Safari, Farhangi, M.B., Mahboubi, A.A., Unc, A.
Agriculture, ecosystems & environment 2010 v.137 no.1-2 pp. 163-171
cattle, cattle manure, Escherichia coli, soil transport processes, clay loam soils, saturated flow, unsaturated flow, soil profiles, soil solution, leaching, adsorption, spatial variation, soil depth, soil texture, soil structure, animal pathogenic bacteria, soil bacteria
Despite relatively extensive laboratory trials, in situ research on transport of bacteria through layered soil is surprisingly lacking. We investigated the in situ transport of cow manure-borne Escherichia coli through a naturally layered clay loam soil profile, under saturated and unsaturated steady flows. Lysimeters (22cm diameter and 50cm height) were inserted vertically into the field soil. Water flow through the columns was controlled by a tension infiltrometer by imposing inlet matric suctions of 5 and 0cm for the unsaturated and saturated conditions, respectively. When the steady-state flow was established, cow manure was applied on the lysimeters' surface at the rate of 10Mgha⁻¹ (dry basis). Soil solution was sampled during leaching at two depths (20 and 40cm) at 1, 2, 4, 6, 12, and 24h after manure application. Concentrations of the bacteria in the influent (C ₀) and soil solution (C) samples were determined. Bacterial filtration coefficients (λ f) and relative adsorption indices (S R) were calculated for each flow condition and soil depth. Flow condition, sampling depth and their interaction had significant effects (P <0.05) on the C and C/C ₀ values for all leaching times except at 24h. At 24h only the flow condition affected significantly the C and C/C ₀. Flow condition and depth affected the λ f and S R. Maximum and minimum values of λ f were calculated for the unsaturated condition/first depth and saturated condition/first depth combinations, respectively. The unsaturated λ f was nearly 34% greater than the saturated λ f. Although the topsoil had significant bacterial filtration capacity, equivalent filtration was measured for the deeper strata. Overall, variation of texture and structure along the in situ soil profile effectively altered the bacteria movement.