The sustainability of cereal cropping systems may be improved by the addition of legumes. The effects of seeding rate were studied for intercrops of berseem clover (Trifolium alexandrinum L.) and oats (Avena sativa L.). Bigbee berseem clover, an annual forage legume, was intercropped with oats on a Black Chernozemic soil at Edmonton, Alberta, in 1996 and 1997. Berseem dry matter (DM) yields were greatly reduced by increasing oat plant density. There was a linear decline in berseem DM with increasing oat DM or oat tiller density. The relationship between oat plant density and berseem DM was nonlinear and varied between years and harvests. Berseem yield reductions varied from 44 to 82% with target densities of 100 oat plants m-2. Effects of berseem seeding rate (BSR) on oats varied between years. Increasing BSR from 6 to 24 kg ha-1 decreased oat tillering, oat DM and oat plant DM by 22–51, 0–57 and 8–51%, respectively, and increased oat tiller DM by 0–18%, with oats at 10 to 20 plants m-2. Differences between years were likely due to environmental factors and relative emergence times. After a silage-stage harvest, oat regrowth was negligible but berseem regrowth averaged 3.1 Mg ha-1 DM. Key words: Cereal-legume intercrop, Trifolium alexandrinum L, Avena sativa L, competition models