Nitrate leaching is of environmental concern in the rain-fed potato production on loamy sands. The current tillage practices in potato fields induce a significant soil and nitrate redistribution during the growing season (Zebarth and Milburn, 2003). To characterize nitrate concentration in soil in potato fields, variations in the hill must be considered. The aim of this study was to characterize nitrate transfer in a potato hill during the growing season and to give estimations of nitrate leaching. Our potato fields were located in southern Quebec in 2004 (wet July) and 2005 (dry July). Total rainfalls from May to September 2004 was 537 mm, the highest value was 160 mm in September with exceptional rain in July (157 mm). In 2005, total rainfall was 747 mm with an exceptional dry July with 91 mm and the highest value of 256 mm in September. An inorganic N application of 160 kg N ha-1 at planting was followed by no N, 45 kg N ha-1, and 90 kg N ha-1 at hilling. Soil cores were collected bimonthly in each plot during 2004 and 2005 summer at four different places in the hill with a high precision in space and the operations were replicated twice in each treatment. For each sampling event, a sampling gear of diameter 2.5 cm and 90 cm long was used to sample half of the hill at four different places from the center of the hill to the furrow for a total length of 45 cm, and each sample was 15 cm spaced from each other. The soil core was cut in the laboratory into nine pieces: 0-5 cm, 5-10 cm, 10-15 cm, 15-20 cm, 20-25 cm, 25-30 cm, 30-45 cm, 45-60 cm, 60-90 cm. Nitrate was extracted with 0.01 M CaCl2 and analyzed by ion chromatography. Nitrate concentrations in 2004 varied from 1 mg NO3-N kg-1 in September to 5089 mg NO3-N kg-1 in June Temporal variations revealed occasions with the highest risk of nitrate leaching in 2004 and 2005. We will describe our sampling procedure to assess differential movements of nitrate related to the hill and we will show an estimation of nitrate leaching between sampling dates. Reference: Zebarth, B. J. and P. H. Milburn 2003. Spatial and temporal distribution of soil inorganic nitrogen concentration in potato hills. Canadian Journal of Soil Science 83(2): 183-195.