The Effects of Slug-Grazing on Trifolium repens and Dactylis glomerata in Monoculture and Mixed Sward

Abstract

In replacement series, Trifolium repens dominated Dactylis glomerata eventually eliminating Dactylis from mixed swards. However, grazing by the slug, Deroceras reticulatum, reduced the yield per plant of Trifolium by as much as 60% enabling Dactylis to coexist. In this grazed sward Dactylis grew better and had a 77% higher nitrogen content than grazed Dactylis in monoculture. An analysis of the dry weight frequency distributions of Trifolium and Dactylis from mixed swards suggested that the improved success of Dactylis in grazed swards was due to a disproportionate increase in the growth of intrinsically more vigorous Dactylis plants. The results demonstrate that invertebrate grazing can shift the balance of competition in mixed swards and may influence the uptake and partitioning of nutrients among plants.