Copper content of soil and herbage following pig slurry application to grassland

Abstract

Recent amendments to European Economic Community Feed Additives Directive 70/524 have lowered the maximum permitted copper content of pig rations because of concern about the environmental pollution risks that may be caused by land application of slurry containing high copper concentrations. The inclusion of copper compounds in pig feed improves growth rates and food conversion ratios, but 80–90% of dietary copper is excreted (Unwin, 1977), although the concentration in slurry varies widely according to diet and water intake. Repeated applications of pig slurry to grassland may result in copper-induced phytotoxicity and, more importantly, toxicity to grazing livestock, particularly sheep. However, the experimental evidence regarding the accumulation of copper in soil and herbage is inconclusive, and there is some difficulty in identifying ‘safe’ levels, as these vary according to soil type, herbage composition and herbage contamination (Batey, Berryman & Line, 1972; Bremner, 1981). Results are presented here on an experimental investigation into soil and herbage copper contents under three different slurry application rates at two permanent grass sites.