I. Influence of lucerne on a cover crop

Three trials were conducted at Lincoln to examine the effect of undersown lucerne on wheat and barley cover crops. Spring‐sown lucerne reduced the grain yield of spring‐sown barley by an average of 11% but had no effect on winter‐sown wheat. In one trial, halving the barley seeding rate reduced yield by an additional 19%, but in another there was a small increase in yield. Causes of competition are discussed, and nutrients, particularly nitrogen, are thought to be dominant factors in interspecific competition.