Genetics parameters and association of NUE methods in maize under different nitrogen levels / Parâmetros genéticos e associação de metodologias de EUN no milho sob diferentes doses de nitrogênio

This work aimed to study the association of four nitrogen use efficiency (NUE) methods and the genetic parameters of grain weight in two groups of maize genotypes, under different levels of nitrogen supply, in the season 2012/13. 16 field experiments were carried out in the city of Gurupi, Tocantins, Brazil. Each genotype group was evaluated in different seeding date, and each one was tested with different levels of nitrogen supply. In all experiments the experimental design was completely randomized blocks with three repetitions. The following trait was evaluated after stage R6: grain yield (GY), and after, four indices of efficiency/stress to nitrogen were estimated. The Pearson correlation coefficients, estimated among the indices, were all significant (P < 0.01). Among the seeding dates, the average heritability of GY was 54.4% and among the levels of nitrogen supply, the following values were observed: 60.4% (low N); 50.9% (medium N); 51.2% (high N). There is the possibility of the use of environments with lower nitrogen supply in the search for superior and more efficient genotypes for the GY, and based on our results, the Low N index is more adequate.