LOSS OF BIOACTIVE PHOSPHORUS AND ENTERIC BACTERIA IN RUNOFF FROM DAIRY MANURE APPLIED TO SOD

Information on the concurrent release and interactions between manure-borne phosphorus (P) and enteric bacteria to runoff from a live or dead grass sod is limited. A study of simulated runoff and an enzyme-based fractionation of runoff P forms from dairy manure applied on grass-covered soil in runoff boxes was conducted to compare the detachment and potential edge-of-field movement of manure P, Escherichia coli, and enterococci in runoff. Concentrations and mass loads of bioactive P forms and bacteria in runoff were log-normally distributed over time during all simulations. Although P and enteric bacteria were simultaneously released to runoff, high correlations were found predominantly between water turbidity, concentrations of bacteria, and phosphohydrolase-labile P, a fraction associated with particulate manure. Delayed bacteria and particulate P concentrations and mass loads indicated live leaf and bacterial surface interactions that impeded their release to runoff. Resultant deviations in linearity between manure water-extractable P and bacteria distributions and the significant correlation between bacteria and the phosphohydrolase-labile P fraction suggested that manure-borne E. coliwere released in association with manure particulates that contained organic P. The state of the grass cover determined the asymmetry of bacteria and bioactive P distributions. Given the micrometer size range of suspended particles, losses of colloidal particulate P and colloid-associated bacteria may extend well beyond the immediate vicinity of the deposited manure.