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Crested wheatgrasses [Agropyron cristatum L. Gaertn. and A. desertorum Fisch. ex (Link) Schult.] have been extensively seeded on semiarid western rangelands, but without supplemental N many of these seedings decline in vigor, ground cover, and productivity as the stand ages. Biological N2 fixation by legumes may represent a viable alternative to fertilizer N for increasing stand productivity. Two growth-room studies were designed to investigate N2 fixation and N transfer in mixtures of alfalfa (Medicago sativa L.) or annual sweetclover (Melilotus alba Medik. var. annua Coe) and crested wheatgrass. Growth media were enriched with 15N-labeled KNO3 at a rate of 24.2 kg N ha-1 and used to grow mixtures and monocultures of alfalfa or sweetclover and crested wheatgrass. Fixed and transferred N were determined at 3 harvest dates from differences in isotopic composition between the legume species in mixture with crested wheatgrass and crested wheatgrass in monoculture. The percentage of legume N derived from fixation was >80% for the final 2 harvests and increased as the proportion of crested wheatgrass in the mixtures increased. Nitrogen transfer from alfalfa to crested wheatgrass accounted for < 5 % of the grass total N. Conversely, nitrogen transfer from sweetclover to crested wheatgrass accounted for about 20% of the grass total N. Nitrogen transfer from alfalfa or sweetclover to crested wheatgrass may be important in maintaining stand productivity on N-limited western rangelands. This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries. The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information. Migrated from OJS platform August 2020