The objective of this experiment was to evaluate the morphogenetic traits and biomass accumulation of Brachiaria brizantha cv. Xaraés subjected to doses of N (0, 125, 250, 375 and 500 kg.ha-1 N). The treatments were arranged in a completely randomized design with four replications. Morphogenetic traits and biomass accumulation of dry matter (DM).ha-1 were evaluated. The results were subjected to statistical analysis by grouping the data in two periods, rainy season and throughout the year. Nitrogen doses influenced leaf appearance in the rainy season and throughout the year, with significant increase in leaf elongation during the rainy season, an increase of 56% compared with control. During this period, maximum dose of N (248.1 kg.ha-1) produced 214.49 kg.ha-1.day-1 DM of leaf blade, which was 133% higher than the control. However, the higher N dose in the rainy season resulted in an increase of 137% in the stalk accumulation compared with non-fertilized grass; estimating maximum accumulation of salk of 84.97 kg.ha-1.day-1 of DM for the application of 326.2 kg.ha-1 N. Doses of N also intensified leaf senescence during the rainy season and throughout the year. The control treatment presented 32% less senescence compared with maximum N dose (270.1 kg.ha-1 N) in the rainy season. Forage loss was estimated at 26.08 kg ha-1.day-1 DM at the maximum dose of 295.0 kg.ha-1 N for this period. All variables studied responded positively to N supply in the rainy season. The accumulation of biomass of the plant reached the maximum point with fertilization close to 250 kg.ha-1 N in the rainy season and 375 kg.ha-1 N throughout the year.

Objetivou-se neste experimento avaliar as características estruturais e agronômicas da Brachiaria brizantha cv. Xaraés sob diferentes doses de nitrogênio (0; 125; 250; 375 e 500 kg.ha-1 de N) cultivadas no Campus Universitário de Rondonópolis, Mato Grosso, no período de 12/10/2006 a 23/8/2007. Os tratamentos foram dispostos em delineamento inteiramente casualizado com quatro repetições. Os resultados obtidos foram submetidos às análises estatísticas agrupando-se os dados em dois períodos, águas e ao longo do ano. As doses de N influenciaram o número de folhas aparecidas para a época chuvosa, assim como o número de folhas verdes. O número de folhas totais foi influenciado pelas doses de N nas águas e ao longo do ano. Houve incremento de 27% no comprimento médio da lâmina foliar para a dose de 343,9 kg.ha-1 de N para o período das águas. A densidade de perfilhos foi influenciada pelas doses de N para ambos os períodos de avaliação, sendo que a altura das plantas foi influenciada pelas doses de N para as duas épocas avaliadas. O aumento na disponibilidade de matéria seca por hectare foi de 87,5% para a maior dose de N nas águas (333,3 kg.ha-1 de N) em comparação ao tratamento testemunha. A adubação nitrogenada influencia positivamente todas as características relacionadas ao crescimento e à produção de massa, principalmente no período chuvoso, quando a adubação deve ser parcelada em quatro ou cinco doses, não justificando adubações no período seco do ano.

The objective of this experiment was to evaluate the structural characteristics and agronomic traits of Brachiaria brizantha cv. Xaraés under different nitrogen levels (0, 125, 250, 375 and 500 kg.ha-1 of N) grown in Campus Rondonópolis, Mato Grosso, in the period 10/12/2006 to 08/23/2007. The treatments were arranged in a randomized design with four repetitions. The results were submitted to statistical analysis by grouping the data into two periods: rain and throughout the year. The N influenced the number of leaves appeared at the time rainy, and the number of green leaves. The number of leaves was influenced by N rates during the rain and throughout the year. There was an increase of 27% in the average length of the leaf blade to the dose of 343.9 kg ha-1 N for the rainy season. The density of tillers was influenced by N rates for both evaluation periods. Since the height of the plants was influenced by N rates for the two seasons evaluated. The increased availability of dry per hectare was 87.5% for the highest N in the water (333.3 kg ha-1 N) compared with the control treatment. Nitrogen fertilization positively influences all characteristics related to growth and production mass, especially during the rainy season, when the fertilization must be divided into four or five doses, with no need for fertilization in the dry season.