Nitrogen (N) is the nutrient taken up in the largest quantity by corn and it has the greatest effect on grain yield. Its dynamics in the soil-plant system is influenced by the management. The aim of this study was to evaluate nitrogen rates and application times in corn in a recently implanted no-tillage system. This study was conducted at the Experimental Station of UNESP/FEIS - Ilha Solteira campus in Selvíria, State of Mato Grosso do Sul, Brazil, during the growth season of 1998/99 and 1999/00 on a clayey dystrophic dark Red Latosol (Rhodic Haplustox). The experimental design was structured in randomized complete blocks, with 19 treatments and 4 replications in an incomplete factorial 6 x 3 + 1 (control: 0 kg ha-1) scheme. Six combinations of N application timing (total dose at sowing, total dose at the 4 - 6 leaf stage, total dose at the 8 - 10 leaf stage, ½ at sowing + ½ at the 4 to 6 leaf stage, ½ at sowing + ½ at 8 to 10 leaf stage and, ½ at the 4 to 6 leaf stage + ½ at the 8 to 10 leaf stage) and 4 rates of N-urea (0, 60, 120, and 180 kg ha-1). Soil samples were collected in the 0.0-0.10, 0.10-0.20 and 0.20-0.40 m layers for an evaluation of N-NH4+, N- NO3-, mineral-N and total-N concentration. Plants were analyzed for plant and ear height, leaf N concentration at flowering and N concentration in the grains, rows of grain per ear, grains per row, weight of thousand grains, and grain yield. The NH4+ content was higher than NO3- at the same depths, in both cultivations. The grain yield of the corn had the highest technical efficiency at the N rate of 166 kg ha-1, and a maximum economical efficiency with 126 kg ha-1 of N, applied half dose at sowing and the remaining at the 4-6 leaf stage, considering a fertilizer cost and corn price ratio of 8.25:1.
No-tillage; mineral-N; total-N; Zea mays L
