No-tillage affects maize (Zea mays L.) fertilizer N use efficiency when urea is surface-applied, due to NH3 volatilization. A 3-year field experiment was conducted at Balcarce, Argentina (37°45′ S, 58°18′ W), on a soil complex of a fine, mixed, thermic Typic Argiudoll and a fine, illitic, thermic Petrocalcic Paleudoll. The objective was to evaluate the effect of surface-applied urea rate (0, 35, 70, 140, and 210 kg N ha−1), with and without a urease inhibitor [N-(n-butyl) thiophosphoric triamide] (nBTPT) at different times (planting; six-leaf stage, V6) on NH3 volatilization losses, soil mineral N, and maize N uptake and grain yield under no-tillage. A semiopen static system was used to monitor NH3 volatilization losses. Ammonia N losses from urea without nBTPT ranged between 2.6 and 13.3% of applied N, being greater with higher N rates and when the urea was applied at V6. Volatilization losses with nBTPT were not different than those from the control. The use of nBTPT did not increase soil mineral N consistently and did not increase N uptake nor grain yield. Relative to fertilization at planting, fertilization at V6 increased soil mineral N at flowering, N uptake at physiological maturity (167 and 155 kg ha−1, respectively), and grain yield (11 003 and 10 440 kg ha−1, respectively). For slightly acid and high organic matter soils, the use of nBTPT did not improve urea N use efficiency. Delayed urea application had a greater and more consistent effect than the use of nBTPT on the increase of no-till maize grain yield and N use efficiency.