The aim of this experiment was to evaluate the N availability for corn and wheat with different methods of N fertilization. The study was carried out at University of Cruz Alta, State of Rio Grande do Sul, Brazil, in an Oxissol under six years of no-tillage. A completely randomized block design with four repetitions was used. Combinations of different times and rates of N application were studied. The times were: application before seeding, at seeding and topdressing. The rates of N for corn were zero, 60 and 90kg ha-1 and for wheat zero, 30 and 60kg ha-1. The amount of soil mineral N decreased quickly after application of N fertilization. The soil´s mineral N content was related to the rates and time of application. The N application time, considering the same rates, splitted or not, didn't influence dry matter production, N accumulation and grain yield. These parameters increase with the rate of N application. The splitting of the N fertilization, part at the seeding time and part as topdressing, is the safest way to minimize the N losses and to maximize the use of N by corn and wheat plants.
mineral nitrogen; nitrogen rates and application time
