May, W. E., Lafond, G. P., Gan, Y. T., Hucl, P., Holzapfel, C. B., Johnston, A. M. and Stevenson, C. 2012. Yield variability inPhalaris canariensisL. due to seeding date, seeding rate and nitrogen fertilizer. Can. J. Plant Sci. 92: 651-669. Concern over the year-to-year and field-to-field variability in grain yield has consistently been expressed by annual canarygrass growers in Saskatchewan. The objectives of these studies were to understand the effects of a delayed seeding date (0, 15, 30 and 45 d), seeding rate (15, 25, 35, 45, and 55 kg ha^-1 of seed) and applied N fertilizer (20, 40, 60, 80, and 100 kg N ha^-1) on the development and yield of annual canarygrass, to improve recommendations of best management practices in annual canarygrass and to determine the impact of these factors on yield variability in annual canarygrass. To address these objectives, three single factor field experiments were conducted, at a number of sites in Saskatchewan from 1998 to 2001. Seeding date had a large effect on grain yield. Grain yield decreased as seeding was delayed by 30 and 45 d from early May. Seeding rate had a small effect on grain yield. The response curve was very shallow peaking at approximately 1310 kg ha^-1 at a seeding rate of 45 kg ha^-1. Variation in grain yield tended to decrease as the seeding rate increased. There was a small increase in grain yield with the addition of nitrogen fertilizer. The response curve estimated a maximum yield of 1215 kg ha^-1, which was obtained with a nitrogen rate of 78 kg ha^-1. The majority of the increase was between 20 and 40 kg N ha^-1, with a 2.3 kg ha^-1 increase in grain yield for each kg of fertilizer N in that range of rates. There was a slight increase in grain yield as the nitrogen rate increased above 40 kg ha^-1 but the variation in grain yield also increased reducing the incentive for growers to use N rates above 40 kg ha^-1. Seeding date had a large effect on seed yield and could impact yield variability while seeding rate and nitrogen rate did not have a large effect on seed yield or yield variability.