The nitrogen supply in wheat cultivation dependent on weather conditions and succession system in southern Brazil

High wheat yields, besides the genetic potential and edaphoclimatic conditions, are obtained by proper management and nitrogen use. The objective of the study was to define the most appropriate time for N-fertilizer application, considering the range of greatest wheat requirements, dependent on the succession system type and the predictability of favorable and unfavorable years. The study was carried out in the 2008 to 2012 years, in Augusto Pestana, Rio Grande do Sul, Brazil. The experimental design was randomized blocks with four replications, with N-fertilizer application at 0, 10, 30 and 60 days after emergence, considering the corn/wheat and soybean/wheat succession system. The study found that the best time for nitrogen fertilizer application on wheat is mostly influenced by the year of cultivation and is less influenced by the succession system type. The appropriate time for the N-fertilizer application in favorable years of cultivation was about 45 days after emergence. In unfavorable years, it must be anticipated. Regardless of the cultivation year and the succession system type, the N-fertilization at 30 days after emergence evidenced the highest means as the most stabile grain yield. Key words: Wheat Triticum aestivum, N-fertilizer time, optimization.