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RESUMO -Avaliaram-se as características morfogênicas e estruturais do dossel de Brachiaria brizantha, cv. Marandu, sob pastejo intermitente no período chuvoso, em diferentes ofertas de forragem e ciclos de pastejo. O delineamento experimental foi em blocos ao acaso, em esquema de parcelas subdivididas, com três repetições. Nas parcelas, avaliou-se o efeito das ofertas de forragem (4, 7, 10 e 13% do PV/dia) e, nas subparcelas, o efeito dos ciclos de pastejo. Todas as variáveis diferiram entre os ciclos de pastejo, comprovando grande influência das condições ambientais sobre as características avaliadas. A taxa de alongamento do colmo e a altura do dossel responderam linear e positivamente ao aumento da oferta de forragem. O número de perfilhos vegetativos nos piquetes com a menor oferta permaneceu constante ao longo de todo o período experimental, no entanto, nos piquetes com as demais ofertas, atingiu valores mais elevados nos ciclos intermediários. A densidade de perfilhos reprodutivos e totais ajustou-se ao modelo quadrático de acordo com a oferta de forragem. Pastos manejados com ofertas de forragem próximas a 4% PV/dia têm menor alongamento de colmos e tendem a reduzir as perdas por senescência. As variáveis ambientais exercem maior influência sobre as características morfogênicas e estruturais em comparação a ações de manejo como a oferta de forragem. block experimental design was used in a split-plot scheme with three replicates. It was evaluated in the plots the plots, the effects of forage supplies (4,7, 10 and 13% BW/day) and in the subplots, the effects of grazing cycles were evaluated. All the variables differed among grazing cycles, proving the great influence of environmental conditions on the evaluated characteristics. Stem elongation rate and canopy height showed linear and positive responses to the increase on forage supply. Number of vegetative tillers in the plots with the lowest supply was constant over the whole experimental period, however, in the plots with the other supplies, tillers reached highest values in the intermediate cycles. Density of total and reproductive tillers was fitted to the quadratic model accordingly to the forage supply. Pastures managed with forage supplies close to 4% BW/day showed lower stem elongation and they tend to reduce loses caused by senescence.Environmental variables affect morphogenetic and structural characteristics more than management with forage supply does.Key Words: Brachiaria brizantha, canopy height, grazing cycles, grazing intensity, morphogenesis, stem elongation IntroduçãoNa busca pela correta condução dos animais em pastejo, é de grande importância o conhecimento do processo de transformação da forragem em produto animal e, principalmente, da dinâmica dos processos de crescimento e desenvolvimento das plantas que compõem a pastagem e suas respostas morfofisiológicas aos fatores interferentes. Entre esses fatores, destaca-se a intensidade de pastejo, que afeta diretamente as taxa de acúmulo de forragem (Parsons et al., 1983).As gramíneas tropica...

Greenhouse gases (GHG) can be affected by grazing intensity, soil, and climate variables. This study aimed at assessing GHG emissions from a tropical pasture of Brazil to evaluate (i) how the grazing intensity affects the magnitude of GHG emissions; (ii) how season influences GHG production and consumption; and (iii) what are the key driving variables associated with GHG emissions. We measured under field conditions, during two years in a palisade-grass pasture managed with 3 grazing intensities: heavy ( 15cm height), moderate (25 cm height), and light (35 cm height) N 2 O, CH 4 and CO 2 fluxes using static closed chambers and chromatographic quantification. The greater emissions occurred in the summer and the lower in the winter. N 2 O, CH 4 , and CO 2 fluxes varied according to the season and were correlated with pasture grazing intensity, temperature, precipitation, % WFPS (water-filled pores space), and soil inorganic N. The explanatory variables differ according to the gas and season. Grazing intensity had a negative linear effect on annual cumulative N 2 O emissions and a positive linear effect on annual cumulative CO 2 emissions. Grazing intensity, season, and year affected N 2 O, CH 4 , and CO 2 emissions. Tropical grassland can be a large sink of N 2 O and CH 4 . GHG emissions were explained for different key driving variables according to the season.

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Soil carbon dioxide emission (ECO2) is a process determined by biotic and abiotic factors in uenced by land use and management practices. In grassland ecosystems, grazing intensity may a ect C input from plants into soil, and thus may also change soil respiration rate. Indeed, limited information is available regarding the e ects of grazing management on ECO2. is study was conducted to evaluate ECO2 seasonal variation, and its relationship to soil temperature (Tsoil) and precipitation, in an area with di erent pasture heights of Marandu palisade grass [Brachiaria brizantha (A.Rich.) Stapf.]. e pasture heights (15, 25, and 35 cm) were distributed in a completely randomized design with 12 repetitions in each area. e evaluations of ECO2 and Tsoil occurred from January 2011 to February 2013, totaling 73 d of observation that were distributed according to climatic seasons. e results showed that seasonal variation of ECO2 was directly related to variations in precipitation and Tsoil. Soil CO 2 emission was higher in summer and lower in winter. e data variability of ECO2 was higher in rainy, hot summers than in dry, cold winters. A positive linear association between ECO2 and Tsoil was observed in summer and autumn. In most seasons measured, ECO2 reduced with increasing pasture height. Accordingly, 2-yr data indicated that accumulated ECO2 decreased with increasing pasture height. us to better understand the e ect of pasture height on ECO2, a shorter period of measurements is not suitable since a di erent result was observed in the rst year of evaluation.