A gronomy J our n al • Volu me 10 0 , I s sue 4 • 2 0 0 8 electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. N arrow-leafed lupin and tannin-free faba bean are new pulse crops for the Parkland region of Alberta, Canada. Since 2002, tannin-free faba bean production has increased due to its high yield, high protein, high energy, a reduction in antinutritional factors (e.g., tannin), and similar production costs relative to fi eld pea (Pisum sativum L.), the traditional pulse crop of the region. A second cool-season pulse crop, narrow-leafed lupin, is also showing promise as a new crop in the region because lupin can provide new market opportunities, a locally grown high protein feed source, and the opportunity to diversify crop rotations.Volunteer barley interference can signifi cantly decrease the productivity of faba bean and lupin. A previous study conducted in northern Alberta, Canada, indicated that faba bean and lupin seed yields were reduced by 42 and 67%, respectively, when these crops were grown in the presence of barley interference (Strydhorst et al., 2008). In Denmark, Knudsen et al. (2004) also documented the competitive eff ects of barley on these two crops. When grown with 150 barley plants m -2 , faba bean comprised 72% of the mixture grain yield compared with a faba bean sole crop, while lupin comprised 36% of the mixture grain yield compared with a lupin sole crop. Th ese studies indicate the sensitivity of faba bean and lupin to volunteer barley interference; however, we are not aware of studies that examined the competitive eff ects of volunteer barley on the physiology of these two crops.In cereal crops, competitive ability has been related to rate of establishment, vegetative growth habit, tillering capacity, and straw height (Richards and Davies, 1991;Lemerle et al., 1996). In addition to these traits, crop biomass at early growth stages can infl uence competitive ability (Richards and Whytock, 1993;Paolini et al., 1998Paolini et al., , 2002. However, previous studies have spent less time measuring canopy architecture and interception of photosynthetically active radiation (PAR), two factors that can greatly infl uence competitive ability. Seavers and Wright (1999) reported that cultivar competitive ability was associated with high overall LAI, canopy structure, and development. Studies documenting the competitive traits of faba bean and lupin are rare.Volunteer barley interference can contribute to signifi cant yield losses; therefore, it is necessary to understand which traits infl uence competitive ability so that agronomic practices can be recommended that will minimize the eff ects of competition. Breeding programs can also focus on selecting traits that will improve the competitive ability of these two crops. Th e objective of this study was to assess the eff ect of volunteer barley density on faba bean and lupin crop DM production by sequentially quantifying crop LAI development...