Nitrogen use efficiency (NUE) in maize may be improved by using a sensor-based nitrogen rate calculator (SBNRC). The objective of our study was to evaluate the NUE in maize fertilized with fixed or variable rates estimated by using a SBNRC. Four experiments (E) were conducted during the 2004-05 (E1 and E2) and the 2005-06 (E3 and E4) growing seasons in Paraná, Argentina. (31.5ºS). E1 and E3 were timely sowed and treatments included combinations of N rates at planting (0, 70, 140 y 210 kg N ha-1) and two strategies to late N fertilization: a fixed rate (FR = 70 kg N ha-1) and a variable rate (SBNRC). In both strategies, N was broadcasted as urea at V8, V10, V12 and V14 growth stages. E2 and E4 were late planted and treatments included N rates at planting (0, 50, 100 and 200 kg N ha-1 in E2 and 0, 70, 140 and 210 kg N ha-1 in E4) and a late N application at V12 using a fixed rate (50 kg N ha-1 in E2 and 70 kg N ha-1 in E4) or a variable rate (SBNRC). Results in E1 and E2 showed that maize grain yield was similar between strategies and NUE was higher with the SBNRC. In spite of a severe drought in the 2005/06 (E3 and E4) season, that significantly reduced crop yield and N response irrespective of N strategy; NUE was higher in the SBNRC. However, despite of promissory results on NUE increases, more studies to improve yield predictions in late planting dates are needed.