This study evaluated the leaf area index (LAI) recovery mechanisms and forage accumulation rates on the regrowth of different grass species subjected to different defoliation intensities. For that purpose, plots of Pennisetum clandestinum (kikuyugrass), Lolium multiflorum (annual ryegrass), and Avena strigosa (black oats) were defoliated from 20 to 80 % of their initial heights (25, 20, and 25 cm, respectively). At different increments in height, forage samples were collected to ground level and used to estimate tiller population density (TPD), leaf area per tiller (L A), and forage mass. From these data, we calculated the leaf area index (LAI), average leaf area index (aLAI), and average and instantaneous forage accumulation rate (FAR and IFAR, respectively). Data were plotted over time (days) to describe LAI recovery and forage accumulation rates. As the defoliation intensity increased, greater canopy heights were needed for pastures to achieve their maximum forage accumulation rates, which required longer regrowth intervals. The need for high tiller recruitment after defoliation, which delayed canopy LAI recovery, seemed to be one of the main cause. Thus, grazing management strategies that involve costly tiller recruitment could decrease both overall forage production and sward persistence over time. However, the plant ability to recover LAI after successive intense defoliations seems to be species-dependent and related to their phenotypic plasticity.

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Resumo -O objetivo deste trabalho foi avaliar o acúmulo de forragem, a estrutura do dossel, o valor nutritivo, o consumo de forragem e a produção animal, em pastos de Urochloa humidicola sob lotação contínua. As cultivares BRS Tupi e Comum foram avaliadas durante os períodos de seca e das águas (julho de 2011 a agosto de 2012), em delineamento experimental de blocos ao acaso, com dois tratamentos e seis repetições. Mensalmente, os animais foram pesados e os pastos amostrados para a determinação de: taxa de acúmulo de forragem (TAF); massa de forragem; percentagens de folha (PF), colmo e material morto (PM); e valor nutritivo. O consumo de matéria seca (CMS) foi determinado uma vez a cada período. 'BRS Tupi' apresentou maiores TAF e PF e menor PM do que a 'Comum', durante o período das águas. O valor nutritivo, o CMS e o ganho médio diário foram semelhantes entre as duas cultivares. O conteúdo de proteína bruta da forragem -6,0 e 5,0%, respectivamente, para os períodos das águas e seco -foi o principal fator limitante ao CMS. 'BRS Tupi' recebeu maior taxa de lotação e, consequentemente, possibilitou maior ganho de peso vivo por área (192 kg ha -1 por ano) do que a 'Comum' (126 kg ha -1 por ano). A 'BRS Tupi' é uma boa alternativa para a diversificação de pastagens em solos de baixa fertilidade sujeitos a alagamento temporário. Termos de indexação:Brachiaria humidicola, Urochloa humidicola, BRS Tupi, estrutura do dossel, quicuio-da-Amazônia, taxa de lotação. Forage intake and animal performance in Urochloa humidicola cultivars under continuous stockingAbstract -The objective of this work was to evaluate forage accumulation, canopy structure, nutritive value, forage intake, and animal production in pastures of Urochloa humidicola under continuous stocking. The cultivars BRS Tupi and Comum were evaluated during the drought and wet periods (July 2011 to August 2012), in a randomized complete block experimental design, with two treatments and six replicates. Monthly, the animals were weighted and the pastures sampled for the determination of: forage accumulation rate (FAR); forage mass; percentages of leaves (PL), culms, and dead material (DL); and nutritive value. Forage intake (FI) was determined once a period. 'BRS Tupi' had a higher FAR, PL, and DL than 'Comum', during the wet period. The nutritive value, FI and the daily weight gain were similar between both cultivars. Forage protein content -6.0 and 5.0%, for the wet and drought periods, respectively -was the main limiting factor for FI. 'BRS Tupi' had higher stocking rates and, consequently, made possible a higher live weight gain per area (192 kg ha -1 per year) than 'Comum' (126 kg ha -1 per year). 'BRS Tupi' is a good alternative for diversification of pastures in soils with low fertility that are temporarily subjected to flooding.Index terms: Brachiaria humidicola, Urochloa humidicola, BRS Tupi, canopy structure, creeping signalgrass, stocking rate. IntroduçãoA braquiária humidícola, ou quicuio-da-Amazônia -Urochloa humidicola (Rendle) Morrone & Zuloaga [Sy...

The effects of different management strategies on improving growth and modifying the botanical composition of C3 and C4 perennial grasses grown in a mixed canopy are underexplored. We aimed to evaluate the botanical composition and vegetation dynamics of a mixed canopy containing kikuyugrass (Pennisetum clandestinum Hochst. Ex Chiov) and tall fescue (Festuca arundinacea Schreber cv. Rizomat) subjected to four grazing management strategies over 22 mo. The experimental design was a randomized complete block in a factorial arrangement (two maintenance canopy heights: grazed to 7 cm in the autumn, or uninterrupted and maintained at 12 or 17 cm) with three replicates. The plots were sampled every month throughout the experimental period; the forage mass data were used to determine the botanical composition and leaf area index of the canopy. Although autumn grazing to 7‐cm height promoted an increase in pasture leaf proportion, it did not represent an effective augment in pasture leaf mass in the following winter–spring season. Canopies heights managed at 17 cm presented a greater proportion of tall fescue in herbage mass (81%) compared with those maintained at 12 cm (73%). Severe defoliation in the autumn delayed the regrowth to 12‐ or 17‐cm canopy heights by approximately 90–120 d in both evaluation years. From a farm‐level perspective, this result would restrict the recommendation of this grazing management strategy because this time lapse would demand that the pastures not be grazed for the 25–33% period of the year compared with the pastures that were not grazed in the autumn.

Some recent papers have recommended moderate intensities of defoliation in order to maximize herbage intake at different time-scales. Most of them, however, did not assess the grazing dynamics of individual tillers during the stocking period. Therefore, the objective of this work was to describe the defoliation dynamics of kikuyugrass (Pennisetum clandestinum Hochst ex. Chiov) pastures subjected to different intensities of defoliation (40, 50, 60, and 70% of the initial height). Twelve 1500 m2 plots were strip-grazed over 24 h, and the frequency and severity of defoliation of individual tillers were assessed in 40 tagged tillers per experimental unit. From these data (n = 1920), we calculated the grazed area in the upper, second, and third horizon, and the total grazed area. We found that the frequency of defoliation by leaf category (expanding, mature, and senescent) increased linearly with the intensity of defoliation, and that reductions in extended tillers could not be used as a proxy to estimate the frequency of defoliation. Moreover, 22% of the second and third horizons were already exploited with intensities of defoliation of 40%, raising the possibility that the exploitation of lower grazing horizons could be more related to stocking density and relatively independent of the grazed area.

ResumoO objetivo deste trabalho foi avaliar o acúmulo de forragem durante o período de ocupação pelos animais em pastos de capim-quicuiu (Pennisetum clandestinum Hochst. Ex. Chiov.) manejados sob lotação intermitente. Os tratamentos consistiram de quatro proporções de desfolhação (remoção de 40, 50, 60 e 70% da altura inicial) partindo de uma mesma altura em pré-pastejo (20 cm). Foram avaliadas: taxas de alongamento foliar e colmos e senescência de folhas, índice de área foliar e taxa de acúmulo de forragem. Adicionalmente, dez perfilhos por faixa foram avaliados para as mesmas variáveis dentro de gaiolas de exclusão. Os efeitos linear, quadrático e cúbico da severidade de desfolhação foram avaliados por contrastes de polinômios ortogonais com 5% de nível de significância. Houve relação linear e inversa entre a porcentagem do índice de área foliar removido e o alongamento de lâminas foliares e o acúmulo de forragem. As taxas de alongamento de folhas em perfilhos bem como o acúmulo de forragem nas áreas excluídas do pastejo foram maiores em relação aos pastos submetidos a desfolhação. Durante o período de rebaixamento de pastos manejados sob lotação intermitente ocorre acúmulo de forragem e o mesmo é linear e inversamente associado à proporção da área foliar removida.Palavras-chave: fluxo de tecidos; índice de área foliar; produção de forragem; severidade de desfolhação; taxa de acúmulo. AbstractThe aim of this study was to evaluate the forage accumulation during the stocking period on Kikuyu grass pastures (Pennisetum clandestinum Hochst. Ex. Chiov) subjected to intermittent stocking. Treatments consisted of four defoliation levels (removal of 40, 50, 60, and 70% relative to the initial height) starting from the same pre-grazing height (20 cm). The following variables were evaluated: leaf and stem elongation rates (evaluated during four times across the period of occupation), leaf area index, and forage accumulation rates. Additionally, ten tillers/strip were evaluated for the same