Biligetu, B., Jefferson, P. G., Muri, R. and Schellenberg, M. P. 2014. Late summer forage yield, nutritive value, compatibility of warm-and cool-season grasses seeded with legumes in western Canada. Can. J. Plant Sci. 94: 1139-1148. In late summer and fall, quality and quantity of forage are important for weight gain by grazing animals in western Canada. The objective of this study was to evaluate forage nutritive value, dry matter (DM) yield, and compatibility of crested wheatgrass [Agropyron cristatum (L.) Gaertn.], meadow bromegrass (Bromus riparius Rehm.), green needle grass [Nasella viridula (Trin.) Barkworth], northern wheatgrass [Elymus lanceolatus (Scribn. & J. G. Sm.) Gould], western wheatgrass [Pascopyrum smithii (Rydb.) Barkworth & D.R. Dewey], Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski], big bluestem (Andropogon gerardii Vitman), or switchgrass (Panicum virgatum L.) in eight grass monocultures, and their binary mixtures with alfalfa (Medicago sativa L.), sainfoin (Onobrychis viciifolia Scop.), or cicer-milkvetch (Astragalus cicer L.) harvested once in August or September. A field study was conducted over a 7-yr period from 1998 to 2004 near Swift Current (lat. 50°25'N, long. 107°44'W, 824 m elev.), SK, Canada, using a randomized complete block design. Forage DM yield was similar between August and September harvests (P>0.05). Binary mixtures of alfalfa-grass produced highest (P<0.05) DM yield ranging from 2449 to 2758 kg ha^-1. The monoculture of crested wheatgrass (2143 kg ha^-1), sainfoin with crested wheatgrass (2061 kg ha^-1), and cicer-milkvetch with green needle grass (1838 kg ha^-1) or cicer-milkvetch with western wheatgrass (1861 kg ha^-1) produced the second highest (P<0.05) DM yields in the ranking. The two warm-season grasses produced the lowest (P>0.05) DM yields over the 7-yr period. Monocultures of green needle grass or northern wheatgrass had the highest acid detergent fiber (ADF) and neutral detergent fiber (NDF), while warm-season grasses with legumes had the lowest. Alfalfa with western wheatgrass and alfalfa with Russian wildrye had the highest crude protein (CP) concentrations. Monocultures of meadow bromegrass, crested wheatgrass, green needle grass, or cicer-milkvetch with meadow bromegrass, and sainfoin with crested wheatgrass had the lowest CP concentrations. In vitro organic matter digestibility (IVOMD) was greater for mixtures than for the grass monocultures. Concentration of Ca and P was greater for warm-season grasses than cool-season grasses. Alfalfa with western wheatgrass was the best combination considering yield, quality, and compatibility for deferred grazing in late summer and fall in the semiarid prairies. Tested warm-season grasses are not recommended for seeding as binary mixtures with legumes for southwestern Saskatchewan.