Fertilizer N has been considered as a source of groundwater pollution because of NO₃-N mobility in soil. This study was conducted on a Torripsammet soil (Valent fine sandy loam) during three consecutive growing seasons to determine the magnitude and differences in NO₃-N losses below corn (Zea mays L.) roots from two different, but current, farmer-used fertilizer management practices. Three farmer-owned and -operated center pivot sprinkler irrigation systems (designated A, B, and C) near Crook, Colo. were used each year. Nitrate-N percolation losses were measured in water samples collected at 150 cm below the soil surface in vacuum extractors located in a line 91, 182, and 372 m for the pivot in each field. The A, B, and C systems were managed so that 4.8, 2.5, and 10.2% respectively, of the growing season water (irrigation plus rain) percolated to the 150-cm depth. Three-year average annual NO₃-N collected in the extractors was 30.4, 19.0, and 59.7 kg/ha for the A, B, and C systems, respectively. Nitrate-N and water percolating to the 150-cm depth were highly correlated (r = 0.95), with each centimeter of water carrying an average 10.2 kg/ha NO₃-N. Average annual total dry matter production for the systems, in the same order, was 20,763, 21,876, and 18,858 kg/ha, respectively, and was negatively related to NO,-N percolating to the 150-cm depth (r = −0.99), showing that production was highly related to NO₃-N loss. Total dry matter production decreased 65 kg/ha for each kg/ha of NO₃-N percolating to the 150-cm depth. Soil NO₃-N changed very little from spring to fall in each of the systems but the soil under the A and B systems contained more than 250 kg/ha NO₃-N to a depth of 180 cm, whereas soil under the C system contained only 20 kg/ha to this depth.