Grazing strategies for reducing contaminant losses to water from forage crop fields grazed by cattle during winter

Abstract

ABSTRACTA paired catchment study quantified fluxes of Nitrogen (N), Phosphorus (P), sediment and Escherichia coli (E. coli) in flow from fields where cattle were wintered on swede (Brassica napus) and kale (Brassica oleracea) crops. The effectiveness of a strategic grazing approach that protected critical source areas was evaluated to determine if these fluxes could be reduced. Reduced soil infiltration caused by cattle treading was a contributing factor to overland flow events that mostly occurred in the six to eight weeks following crop grazing. Estimated annual fluxes of contaminants in overland flow ranged up to 27, 3.8 and 3740 kg ha−1 for N, P and sediment, respectively, and up to 4.3 × 1010 MPN ha−1 for E. coli. Strategic grazing significantly reduced overland flow volumes compared to standard grazing practice, reducing contaminant fluxes to levels similar to those observed when the catchments were returned to pasture and lightly grazed by sheep.