Soil samples to a depth of 100 cm at 20-cm increments for 14 different soil profiles were collected from each of three different soil series on the research farm of the agricultural faculty. Residual soil NO3-N was measured in the samples. In two soil series out of three, a striking zone of NO3-N accumulation was observed in the 20-40 cm depth increments, caused by the differences in texture, moisture conditions, topography, and cultural practices among the soils. Due to the large vertical and horizontal spatial in NO3-N distribution throughout the profiles, it is difficult to recommend a specific number of borings at a given level of precision and probability. However, a discrete value corresponding to the mode for each profile may be recommended as the number of borings to be made. For ''ample, at a precision level of +/- 2.5 kg N/ha, the corresponding number of borings for 95% and 90% probabilities are 11 to 14 and 7 to 9 for Arik, 18 to 20 and 13 for Menzilat, and 11 to 14 and 7 to 9 for Kiziltapir soils, respectively.