Restricting the grazing time of cattle to decrease phosphorus, sediment and E. coli losses in overland flow from cropland

Abstract

This study investigated the effects of grazing management of brassica crops during winter on soil physical properties and sediment, phosphorus (P), and E. coli loss via overland flow. Dairy cows were allowed either unrestricted grazing, grazing restricted to 3 h, or no grazing. Treading in the unrestricted treatment decreased soil bulk density and saturated hydraulic conductivity (Ksat), and increased surface roughness, loads and concentrations of suspended sediment, and E. coli and P loss in overland flow relative to the ungrazed treatment. Only bulk density was different in the restricted compared with the ungrazed treatment. For total P, the mean load in overland flow from the unrestricted grazing treatment after grazing was 3.31 mg/plot compared with restricted grazing (0.74 mg/plot) and ungrazed (0.76 mg/plot) treatments, with most of the increase in particulate form. E. coli concentrations only exceeded water quality guidelines in the first event after grazing, and only in the unrestricted grazing treatment. We found that restricting grazing on forage crops during winter was beneficial for minimising contaminant loss.