Studies about soil nitrogen dinamics and availability are rare in Paraná, the largest corn producer State of Brazil. In its Southwest region the majority of farmers use both corn and soybeans as cashcrops, cultivated under no-till. However reccomendations are poorly made and based only in the soil organic matter content. The objetive of this study was evaluate sidedress urea ( 0, 60, 120 e 240 kg ha-1 of N) fertilization on the nitrate and amonium leves in an acidic oxisol cultivated with corn (cv. Dekalb 215) under no-till. A field experiment under ramdomized blocks design was conducted during 2002/2003, in Pato Branco, PR, Brasil in an area double cropped under no-till during more than 10 years with corn, soybeans, forrage cabbage and winter grain crops. Soil samples were taken from the following depths: 0,0 - 5,0 cm; 5,0 - 10 cm e de 10,0 - 20,0 cm. The leaf and total plan N levels were evaluated and absorption curves were built.