Competition between grasses and legumes in established pastures

The purpose of this chapter is to examine the factors most likely to influence the dynamic grass-legume relationships in established pastures. Attention has necessarily been focused on the economically important ryegrass (Lolium perenne)-white clover (Trifolium repens) mixtures and on work conducted in the British Isles and New Zealand (with their different seasonal growth patterns and management practices). Reference has also been made to supporting Australian observations on subterranean clover (Trifolium subterraneum, a winter-growing annual) where this is appropriate. The intention is to use these studies to show how the results obtained may provide answers not only to the essentially agronomic questions originally raised but also to more fundamental questions about the factors that control grass-legume relationships and, in particular, about the role of N in this relationship.