McKenzie, R. H., Bremer, E., Middleton, A. B., Pfiffner, P. G. and Woods, S. A. 2011. Optimum seeding date and rate for irrigated cereal and oilseed crops in southern Alberta. Can. J. Plant Sci. 91: 293-303. High crop productivity is essential for irrigated crops and may be strongly affected by decisions of seeding date and rate. An irrigated field experiment was conducted at two locations in southern Alberta for 4 yr to compare the impact of seeding date and rate on productivity and quality of nine cereal crops and two oilseed crops. Seeding rate was only evaluated on one date in late April or early May, when maximum yields were expected. Delayed seeding reduced crop yields by 0.6 to 1.7% per day after the end of April: flax (Linum usitatissimum L.) = CWRS wheat (Triticum aestivum L.), feed triticale (×Triticosecale W.) = CPS or SWS wheat = triticale or barley (Hordeum vulgare L.) silage = durum (T. turgidum L.), feed or malt barley < canola (Brassica napus L.). Crop quality deteriorated with delayed seeding for some crops, particularly canola, malt barley and SWS wheat, but was unaffected or even slightly improved for other crops. Seeding rate generally had a smaller effect on crop yield or quality than seeding date, but triticale and SWS wheat required high seeding rates to achieve maximum yields. Early seeding and a sufficient seeding rate were required for high crop productivity of irrigated cereal and oilseed crops in southern Alberta.