response of potatoes to variable nitrogen management by landform element and in relation to petiole nitrogen Á A case study. Can. J. Plant Sci. 92: 771Á781.Recent increases in the cost of fertilizer N have prompted producers to assess the potential to vary inputs within fields and during the growing season to produce the highest marketable yield of potatoes (Solanum tuberosum L.). A study was conducted from 2005 to 2007 near Brandon, Manitoba, Canada, to assess the spatial variability of potato yield in upper, middle and lower landform elements on a sandy loam soil in response to a range of N fertilizer rates applied in the spring or in combination with an application during the growing season. There was no clear trend with respect to the effect of landform on potato yield. Nitrogen fertilizer increased total and marketable yield relative to the control at rates from 75 to 225 kg ha (1 in split applications or applied at seeding. No significant interaction between landform and fertilizer treatment was observed. Petiole N concentration, determined late in the growing season, was correlated with potato yield though the correlation varied considerably between years. Petiole leaflet N concentration was affected by fertilizer on most sampling dates, but decreased with time during the growing season. We conclude that although N fertilizer could be applied during the growing season based on petiole leaflet N concentration deficiencies in mid-July, there is no clear difference in potato yield due to split application relative to spring applications of N fertilizer at rates of 75 kg ha (1 or greater based on landform elements for potato production, likely due to the short growing season in western Canada. Key words: Potato yield, spatial variability, nitrogen management Moulin, A. P., Cohen, Y., Alchanatis, V., Tremblay, N. et Volkmar, K. 2012. Variation du rendement de la pomme de terre en fonction d'une gestion de l'azote d'apre`s le relief et la concentration d'azote dans le pe´tiole Á une e´tude de cas. Can. J. PlantSci. 92: 771Á781. L'escalade re´cente du prix des engrais azote´s incite les agriculteurs a`examiner s'ils pourraient modifier la quantite´d'engrais applique´e dans les champs de pommes de terre (Solanum tuberosum) et durant la pe´riode de croissance, cela dans l'espoir d'obtenir le meilleur rendement possible en tubercules commercialisables. De 2005 a`2007, les auteurs ont proce´de´a`une e´tude pre`s de Brandon, au Manitoba (Canada), afin d'e´valuer la variabilite´du rendement de la pomme de terre dans l'espace, c'est-a`-dire en terrain e´leve´, plat et creux. Les pommes de terre ont e´te´cultive´es sur un loam sablonneux et la culture a e´te´bonifie´e avec un taux variable d'engrais N, applique´au printemps uniquement ou au printemps et pendant la pe´riode ve´ge´tative. Le relief ne pre´sente aucune incidence nette sur le rendement. Les engrais azote´s augmentent le rendement global en tubercules et le rendement en tubercules commercialisables, comparativement aux parcelles te´moins quand on applique 75 ...