Yield response of two potato culivars to supplemental irrigation and N fertilization in New Brunswick

Nitrogen and water are important factors influencing potato production, and crop response to these two factors may vary with cultivars. The yield response of two potato cultivars (Russet Burbank and Shepody) to six rates of N fertilization (0-250 kg N ha^-1) with and without supplemental irrigation was studied at four onfarm sites in each of three years, 1995 to 1997, in the upper St-John River Valley of New Brunswick, Canada. On average, irrigation increased total yield from 31.9t ha^-1 without irrigation to 38.41 ha^-1 with irrigation and marketable yield from 25.61 ha^-1 without irrigation to 30.71 ha^-1 with irrigation. Potato yields were increased by irrigation at nine out of the 12 sites, and the irrigation response was similar for both cultivars. Nitrogen fertilization significantly increased both total and marketable yields at all sites except one. The yield response to N fertilization was greater with irrigation. The N fertilization rate (Nmax) required to reach maximum total and marketable yield, however, was similar with and without irrigation. A large variation in Nmax was observed among sites. With irrigation Nmax varied between 158 and 233 kgN ha^-1 for total yield, and between 151 and 250 kg N ha^-1 for marketable yield. There was no interaction between N fertilization and potato cultivar for both total and marketable yields. The two cultivars had similar total yields (35 t ha^-1). Shepody, however, had a greater marketable yield (28.9 t ha^-1) than Russet Burbank (27.4 t ha^-1). Our results indicate that the response to two of the most significant factors of potato production, irrigation and N fertilization, varies greatly with sites and climatic conditions, and that field specific recommendations are required for the optimum management of N and irrigation.