Fertilization is the factor that presents the highest contribution to corn yield, and may also affect grain quality. The objective of this work was to evaluate, in a an Ultisol, the fertilization with N, Mo and Zn on to determine yield and maize grain quality (protein and mineral nutrient contents) and to determine the best sampling time to analyse organic-N, NO3--N and total-N (NO3--N + organic-N). In addition, nutrient concentrations in maize grain were related to leaves. The experiment was a factorial 4x2x2 in a randomized complete block design with four replications in which the factors were: four N raes (0, 70, 140 and 210 kg ha-1), two of Mo (0 and 90 g ha-1) and two of Zn (0 and 3 kg ha-1). Leaves were sampled 25, 45 and 63 days after emergency (DAE). Tissue and grain were milled and analysed, and organic-N, NO3--N, total-N, protein, P, K, Ca, Mg, S, Zn, Fe, Cu and Mn contents were evaluated. Zinc and molybdenum applications and their interactions with N did not affect any yield characteristics. The weight of thousand grains, the number of ears per plant, the weight of ears with and without straw, and yield increased with increased rates. Maximum yield (8.58 t ha-1) was obtained with 201.2 kg ha-1 N. Protein content and analysed nutrients in grain increased with increasing N rate. Mo fertilization raised protein content, while Zn application increased protein content in grains. The critical levels of total-N were 2.73 and 2.00 dag kg-1 at 45 and 63 DAE. The best traits for diagnosis index and yield prediction was the organic-N content at 45 DAE. In general, grain mineral content was positively correlated with leaft mineral content at 63 DAE.
Zea mays; fertilization; protein content; mineral content