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. 2004. Nitrogen use efficiency characteristics of commercial potato cultivars. Can. J. Plant Sci. 84: 589-598. One approach for reducing the contribution of potato (Solanum tuberosum L.) production to nitrate contamination of groundwater is to develop cultivars which utilize N more efficiently. In this study, variation in N use efficiency (NUE; dry matter production per unit crop N supply) characteristics of 20 commercial potato cultivars of North American and European origin were evaluated in 2 yr. Cultivars were grown with or without application of 100 kg N ha -1 as ammonium nitrate banded at planting. The recommended within-row spacing was used for each cultivar and no irrigation was applied. Plant dry matter and N accumulation were determined prior to significant leaf senescence. Crop N supply was estimated as fertilizer N applied plus soil inorganic N measured at planting plus apparent net soil N mineralization. Nitrogen use efficiency decreased curvilinearly with increasing crop N supply. Nitrogen use efficiency was lower for early-maturing cultivars compared to mid-season and late-maturing cultivars. A curvilinear relationship was obtained between plant dry matter accumulation and plant N accumulation using data for all cultivars. Deviations from this relationship were interpreted as variation in N utilization efficiency (NUtE; dry matter accumulation per unit N accumulation). Significant differences in NUtE were measured among cultivars of similar maturity. Nitrogen uptake efficiency (NUpE; plant N content per unit crop N supply) and soil nitrate concentration measured at plant harvest were uniformly low for all cultivars when crop N supply was limited, but varied among cultivars when N was more abundant. This suggests that potato cultivars vary more in terms of N uptake capacity (plant N accumulation in the presence of an abundant N supply) than in terms of NUpE. Les variétés ont été cultivées avec ou sans application latérale de 100 kg de N par hectare sous forme de nitrate d'ammonium. Les auteurs ont respecté l'écartement recommandé pour chaque cultivar et n'ont pas irrigué la culture. Ils ont déterminé la quantité de matière sèche dans la plante et l'accumulation de N avant une trop forte sénescence des feuilles. La quantité de N fournie aux plantes a été estimée à partir de l'engrais appliqué et de la concentration de N minéral dans le sol à la plantation, plus la minéral-isation nette apparente de cet élément. L'efficacité de l'assimilation de l'azote diminue de façon curviligne avec la hausse de la quantité de N disponible. Les cultivars hâtifs assimilent moins bien l'azote que les cultivars de mi-saison ou tardifs. Lorsqu'on analyse les données venant des différents cultivars, on remarque une relation curviligne entre la quantité de matière sèche et celle de N accumulées par la plante. Les écarts à cette relation sont attribués à une variation dans l'efficacité de l'assimilation du N (EAsN; accumulation de matière sèche par unité de N accumulée). L'EAsN présente d'importantes variations entre le...

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Estimation of optimum fertilizer rates is of interest because of growing economic and environmental concerns. Optimum fertilizer rates can be determined by fitting statistical models to yield data collected from N fertilizer experiments. We evaluated quadratic, exponential, and square root models describing the yield response of potato (Solanum tuberosum L.) to six rates of N fertilization (0–250 kg N ha−1) with and without supplemental irrigation at four on‐farm sites in each of three years (1995 to 1997) in New Brunswick, Canada. Economic optimum N rates (Nop) varied among sites and models. The proportion of variability (R2) explained by the three models was similar. The quadratic model, however, calculated a greater Nop value (175 kg N ha−1) averaged over all sites than those calculated by the square root (123 kg N ha−1) and exponential (80 kg N ha−1) models. Regression residues of the quadratic model were closer to a normal distribution than those of the other two models, indicating a less systematic bias. Economic losses were greatest when the quadratic model was the most appropriate model, but the data were fitted to the exponential (loss of $204–240 ha−1; all values in Canadian dollars) or square root model (loss of $58–201 ha−1). We conclude that the quadratic model is the most appropriate for describing the potato yield response to N fertilizer and predicting Nop for areas with a ratio of the cost of N fertilizer to the price of potatoes similar to that in Atlantic Canada.

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