RESUMO -Objetivou-se avaliar a produção de massa seca das folhas, a relação folha/colmo e alguns índices de crescimento do capim-xaraés submetido a doses de nitrogênio (N) e potássio (K). O experimento foi conduzido em casa-de-vegetação no período de novembro/2004 a fevereiro/2005. Adotou-se esquema fatorial 4 × 3, perfazendo 12 combinações, as quais foram distribuídas em delineamento experimental inteiramente casualizado, com quatro repetições, perfazendo um total 48 unidades experimentais. Foram utilizadas quatro doses de N (0, 75, 150 e 225 mg dm -3 ) e três doses de K (0, 50 e 100 mg dm -3 ). Verificou-se efeito das doses de N na produção de massa seca das folhas e na produção de massa seca total, em todos os cortes, com maior produção nas doses mais elevadas de N, ao passo que o K influenciou essas variáveis apenas no segundo corte. A relação folha/ colmo, a RAF, a AFE e a RPF somente foram significativas no terceiro corte da planta. Os efeitos das doses de foram decrescentes sobre essas variáveis, enquanto as doses de K agiram de modo antagônico às doses de N sobre a RAF e AFE.Palavras-chave: área foliar específica, nutrição mineral, razão de área foliar, razão de peso foliar Dry matter production, leaf/stem ratio and growth indexes of palisade grass (Brachiaria brizantha cv. Xaraés), cultivated with different rate combinations of nitrogen and potassiumABSTRACT -This work aimed to evaluate dry matter production, leaf/stem ratio and growth indexes of palisade grass cv. Xaraés grown under increasing nitrogen and potassium rates. The experiment was carried out in a greenhouse from November, 2004 until February, 2005. The experimental treatments consisted of a 4 × 3 factorial arrangement between nitrogen and potassium rates respectively. Nitrogen rates were 0, 75, 150, and 225 mg dm -3 , whereas potassium rates were 0; 50 and 100 mg dm -3 . The experiment design was completely randomized with four replications. It was verified a positive N fertilization effect both on leaf dry matter yield and total dry matter yield. Potassium influenced these same response variables only at the second harvest. The leaf/stem ratio, leaf area ratio (LAR), specific leaf area (SLA) and, leaf weight ratio (LWR) were affected by treatments only at the third harvest. Increasing N rates reduced these response variables (L/S, LAR, SLA, LWR) while potassium rates behaved in an antagonistic way on LAR and SLA.Key Words: leaf area ratio, leaf weight ratio, mineral nutrition, specific leaf area IntroduçãoAs folhas constituem-se em órgãos das plantas responsáveis pela fotossíntese, além de serem a principal fonte de nutrientes para os ruminantes em sistemas de pastejo. Evidencia-se, dessa maneira, a necessidade de se investigarem os modelos morfofisiológicos que se tornam indispensáveis para a definição de estratégias de manejo de pastos.As porções verde da planta são as mais nutritivas da dieta e consumidas preferencialmente pelos animais (Wilson & t'Mannetje, 1978). Segundo esses autores, alta relação folha/colmo representa forragem com ...

In ruminant-forage systems herbage allowance (HAL) has a major impact on grazing intensity and sward structure, affecting animals, plants, and ultimately, pasture yield. Data on HAL responses of tropical cultivated pastures are scarce and this information may be useful in optimizing pasture utilization. The objective of this study was to describe and contrast sward structure and herbage accumulation responses of 'Marandu' palisadegrass [Brachiaria brizantha (A.Rich.) ESTRUTURA DO DOSSEL E PRODUÇÃO DE FORRAGEM EM PASTAGENS DE CAPIM MARANDU [Brachiaria

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Indirect, non-destructive methods for estimating herbage mass on pasture may help growers to better estimate herbage mass and manage the grazing process. The objective of this study was to evaluate two methods for estimating herbage mass on Marandu palisadegrass [Brachiaria brizantha (A. Rich.) Stapf] pastures, over two grazing seasons. The relationships between herbage mass and two indirect, non-destructive measurements (sward surface height -SSH and rising plate meter -RP) were analyzed via regression analysis. Mean determination coefficients (r 2 ) for the regression models were 0.82 and 0.91 for RP and SSH, respectively. Time within season influenced both slope (b) and intercept (a) of the regression models in both methods. The change in model parameters over the course of the seasons suggests the need for frequent model revision and revalidation. Key words: Brachiaria brizantha, sward surface height, herbage allowance, rising plate meter, linear regression QUANTIFICAÇÃO DA MASSA DE FORRAGEM EM PASTOS DE CAPIM MARANDU SOB LOTAÇÃO ROTATIVACOM O USO DE MÉTODOS INDIRETOSRESUMO: Métodos indiretos e não-destrutivos para a estimativa da massa de forragem no pasto podem auxiliar o manejador no estabelecimento de estratégias ótimas de pastejo. O objetivo deste trabalho foi avaliar métodos indiretos de estimativa de massa de forragem em pastos de capim Marandu [Brachiaria brizantha (A. Rich.) Stapf] sob lotação rotativa durante dois anos. Para descrever as relações entre massa de forragem e dois métodos testados (altura do dossel e disco ascendente) foram empregadas regressões lineares. As equações geradas apresentaram coeficiente de determinação médio (r 2 ) de 0,82 e 0,91 para o disco e altura, respectivamente. A época do ano exerceu influência sobre o coeficiente angular (b) e o intercepto (a) das regressões de ambos os métodos. Essa alteração dos componentes das curvas ao longo do tempo indica a necessidade de freqüente revalidação dos modelos. Palavras-chave: Brachiaria brizantha, altura de dossel, oferta de forragem, disco ascendente, regressão linear

The use of a rapid and accurate method in diagnosis and classification of species and/or cultivars of forage has practical relevance, scientific and trade in various areas of study. Thus, leaf samples of fodder plant species Brachiaria were previously identified, collected and scanned to be treated by means of artificial vision to make the database and be used in subsequent classifications. Forage crops used were: Brachiaria decumbens cv. IPEAN; Brachiaria ruziziensis Germain & Evrard; Brachiaria Brizantha (Hochst. ex. A. Rich.) Stapf; Brachiaria arrecta (Hack.) Stent. and Brachiaria spp. The images were analyzed by the fractal descriptors method, where a set of measures are obtained from the values of the fractal dimension at different scales. Therefore such values are used as inputs for a state-of-the-art classifier, the Support Vector Machine, which finally discriminates the images according to the respective species.

Resumo -O objetivo deste trabalho foi avaliar a eficiência de pastejo, o desaparecimento de forragem e a variabilidade espacial do dossel em pastagens de capim-marandu sob diferentes ofertas de forragem em pastejo realizado com bovinos da raça Nelore, em Pirassununga, SP. O delineamento foi em blocos completos ao acaso e os tratamentos consistiram de 5, 10, 15 e 20 kg de massa de forragem por 100 kg de peso vivo (PV) por dia (%), aplicados em lotação rotativa. A taxa de desaparecimento de forragem respondeu positivamente ao aumento da oferta de forragem, oscilando de 2,3 a 6,5 kg de forragem por 100 kg de PV por dia em 2003 Grazing efficiency on marandu palisadegrass as affected by herbage allowanceAbstract -The objective of this work was to evaluate grazing efficiency, herbage disappearance and spatial variability of the sward in Marandu palisadegrass pastures rotationally stocked by yearling Nelore heifers at four levels of herbage allowance, in Pirassununga, SP, Brazil. The experimental treatments were 5, 10, 15, and 20 kg dry matter per 100 kg live weight per day (%), in a randomised blocks design. Herbage disappearance rate increased with rising herbage allowance, and wide-ranging from 2.3 to 6.5 kg DM per 100 kg LW per day in 2003, and from 2.3 to 6.2 kg DM per 100 kg PV per day in 2004. Conversely, herbage disappearance per area differed among treatments only in 2004, and was highest at 20% of herbage allowance (44 kg ha -1 per day). Grazing efficiency decreased with rising herbage allowance, averaged 64% in 2003 and 55% in 2004 for 5% of herbage allowance. The increasing herbage allowance shows as consequence the increase herbage disappearance rate and an exponentially decrease of grazing efficiency.

Numa pastagem degradada de capim-Tobiatã (Panicum maximum Jacq cv. Tobiatã), em Pirassununga - SP, instalou-se um experimento para verificar os efeitos de doses e tipos de calcário com ou sem incorporação, sobre o perfilhamento, a cobertura vegetal e a produtividade da pastagem durante seis cortes no período de 1996 a 1997. A produção de matéria seca não respondeu a tipos e doses de calcário, no entanto, a prática da incorporação com grade mostrou-se efetiva e, no tocante aos cortes, houve acréscimo de produção no verão e redução no inverno. A cobertura vegetal apresentou 72,8% de ocupação para planta forrageira e indicou tendência de menores áreas de solo descoberto nos tratamentos com calcário calcinado.

Photosensitization is severe dermatitis or oxidative/chemical changes in the epidermal tissues activated by the light-induced excitation of molecules within the tissue. It is a series of reactions mediated through light receptors and is more common when the plant-produced metabolites are heterocyclic/polyphenols in nature. The areas affected are exposed body parts and mostly non-pigmented areas with least ultraviolet protection. Similarly, cellular alteration also occurs in the affected animal's dermal tissues and body parts and grazing animals by the accumulation and activation of photodynamic molecules. Photo-oxidation can also occur within the plant due to the generation of reactive oxygen species causing damage and degradation in the form of free radicals and DNA. During the last few decades, many new tropical grass species have been introduced in the grazing lands which are genetically modified, and the animals grazing on them are facing various forms of toxicity including photosensitization. The plant's secondary metabolites/drugs may cause toxicity when bacteria, viral agents, fungi (Pithomyces chartarum), or neoplasia injures the liver and prevents the phylloerythrin excretion. All these may disturb the liver enzymes and blood profile causing a decrease in weight and production (wool and milk etc.) with severe dermal, digestive, and nervous problems. Recent advancements in OMICS (cellomics, ethomics, metabolomics, metabonomics, and glycomics) have enabled us to detect and identify the plants' secondary metabolites and changes in the animal's physiology and histopathology as a causative of photosensitivity. The review focuses on types of photosensitization, reasons, secondary metabolic compounds, chemistry, and environmental effect on plants.