Mohr, R. M. and Tomasiewicz, D. J. 2012. Effect of rate and timing of potassium chloride application on the yield and quality of potato (Solanum tuberosumL. ‘Russet Burbank’). Can. J. Plant Sci. 92: 783-794. Potassium is frequently applied to irrigated potato in Manitoba. Field experiments were conducted at two sites in each of 2006, 2007 and 2008 to assess effects of rate and timing of potassium chloride (KCl) application on the yield, quality, and nutrient status of irrigated potato (Solanum tuberosum ‘Russet Burbank’) in southern Manitoba. Preplant application of KCl increased total and marketable yield at one site, and tended (0.05<P = 0.10) to increase total and marketable yield at three additional sites. At three of the four K-responsive sites, soil test K levels were <200 mg NH₄OAc-extractable K kg^-1, the level below which K fertilizer is recommended based on existing guidelines. Effects of timing of KCl application on total and marketable yield were limited although, averaged across sites, KCl applied at hilling reduced the yield of small tubers (<85 g) and increased the proportion of larger tubers (170 to 340 g) compared with preplant application. Averaged across sites, KCl applied preplant or at hilling reduced specific gravity compared with the 0 KCl treatments. Improvements in fry colour with KCl application were evident at only one site. Petiole and tuber K and Cl^- concentration, K and Cl^- removal in harvested tubers, and post-harvest soil test K concentration increased with KCl application. However, petiole K concentration measured 82 to 85 d after planting predicted only 24% of the variability in relative marketable yield for sites containing between 164 and 632 mg NH₄OAc-extractable K kg^-1 to 15 cm. Results demonstrate the potential for yield increases and specific gravity declines with KCl application under Manitoba conditions, but suggest that further research will be required to better predict the potential for yield responses using soil and petiole testing.