Nitrogen is the most easily absorbed nutrient by corn crop and has the largest effect the yield. The unplowed soil and cultivation of green manure in fallow ground alters the dynamics and the recovery of N by corn in the soil-plant system. Corn is the main crop in terms of cultivated area for grain production in the Cerrado (Savannah) soil and an option for rotation with soybeans. These soils present low N supplying capacity, because of low content of organic matter. The research was carried in a dystrophic red Latosol, southern cerrado (Selvíria-MS), during the 2002/03 growing season. This research is a repetition of one carried out in the previous year in a nearby area, i.e., same soil (*), due to and great dynamic of N in the soil, especially in Cerrado, affected by climatic seazonal variation. The objective of this work was to evaluate the best rate and time and of N application for corn crop and N utilization, using urea-15N, by corn crops grown under no-tillage system in succession to green manures sun hemp(Crotalaria juncea) and millet (Pennisetum americanum) and to the fallow ground; and evaluate utilization of N from soil and the green manures labeled with 15N by corn grown under different N rates. The experimental design was randomized complete blocks, with 24 treatments and four replications in an incomplete factorial, 3x3x2 + 6, three N rates: 80, 130 and 180 kg N ha-1; three preceding cover crops (green manures): sun hemp, millet and fallow ground; two N application time: 4 leaf or 8 leaf stage; and six additional treatments (three without N application and three that received 30 kg N ha-1 at seeding). For the green manures, above ground dry matter yield, amount of accumulated N and the isotopic enrichment were considered, which were, respectively, 8.61 Mg ha-1, 189.0 kg N ha-1 and 1.882 atoms% of 15N for sun hemp; and 6.33 Mg ha-1, 64.0 kg N ha-1 and 2.416 atoms% of 15N for the millet. The spontaneous vegetation produced in the fallow ground plots was 2.86 Mg ha-1 of dry matter, accumulating the equivalent to 33.9 kg N ha-1. The sun hemp provided the highest amount of N derived from fertilizer to corn crop grown in succession , N utilization efficiency and grain yield. The application of N at corn 4 leaf stage provided highest grain yield in succession to millet, compared to the application with 8 leaf stage, being indifferent for corn in succession to sun hemp and fallow ground soil. The increasing nitrogen fertilizer rate increased linearly the utilization of N by corn from sun hemp, and adjusted to quadratic model for N from millet, in average 15.8% (29.8 kg N ha-1) for sum hemp, and 10.4% (6.6 kg N ha-1) for millet. The amount of N derived from of urea fertilizer increased with increasing N rate and reduced the N utilization efficiency, in average 53%, 47% and 45% for the corn grown in succession to sum hemp, fallow and millet, respectively. The soil supplied larger amount of N for the corn compared to the inorganic fertilizer and green manure jointly, being, in average of 119, 116 and 106 kg N ha-1 for the corn grown in succession to sum hemp, fallow and millet, respectively. The results of present experiment corroborate the previous year obtainned information. Research supported by FAPESP, IAEA and CNPq (fellowships).