Sources and rates of nitrogen in summer corn under no-tillage on winter cover crops

Cover crops occupy and protect the soil during winter and also provide nutrients to tropical soils. The aim of this study was to evaluate the effect of sources and levels of nitrogen applied to a summer corn crop cover in succession to cover cropsunder no-tillage. The experimental design consisted of randomized blocks with four replications in a scheme with subdivided plots. The main plot was composed of two crops that preceded corn; common oat (Avena strigosa Schreb.) and forage turnip (Raphanus sativus), and a winter fallow area (weed). The subplot consisted of two nitrogen sources (urea and ammonium sulphate), and the splits of each subplot were constituted by four rates of nitrogen (0, 30, 60 and 120 kg ha-1). The following production components were analyzed: ear diameter, kernel rows per ear, mass of 1000 grains and grain yield. Corn grown after oat presented responses to nitrogen fertilization for mass of 100 grains and hence to grain yield. Key words:  Zea mays, nitrogen fertilization, urea, ammonium sulphate.