Many factors can contribute the nitrogen use efficiency in corn (Zea mays L) genotypes, like weather and soil, for instance. This present study aimed to identify efficient genotype using nitrogen across three seeding date and two covered nitrogen level at Tocantins-Brazil, during the season 2009/2010. The assessment characteristic were through: ear of corn yield and grain yield (kg ha-1), they were correct for 13% of humidity; agronomic nitrogen use efficiency (NUEA), partial by Moll et al and Low N index by Fischer et al. It was done through analysis of variance, considering the fixed genotype effect and the other random. Significant genotype, seeding date, covered nitrogen level, genotype x seeding date and genotype x covered nitrogen level were observed for ear of corn yield, grain yield, NUEA. The NUEA was significantly lower at LN than at HN for all genotypes. At LN the genotypes showed an average of 206 kg of produced grains for each N kg applied (kg kg-1). At HN they showed an average of 39 kg kg-1. The genotypes GEN 03, GEN 10 and GEN 16 were the most efficient that used the nitrogen, in both assessments methods above. It could be concluded that the choice of the methodology may be function of the study purpose, nitrogen level or seeding date effect
