Desenvolveu-se este estudo com o objetivo de avaliar o acúmulo de forragem e as características morfogênicas e estruturais do capim-marandu submetido a combinações de alturas e intervalos de corte. O experimento foi realizado no período de agosto de 2003 a abril de 2004. Os tratamentos corresponderam a combinações entre duas alturas (15 e 30 cm) e três intervalos de corte (tempo correspondente para o aparecimento de três, quatro e cinco folhas por perfilho) e foram alocados às unidades experimentais em arranjo fatorial 2 × 3 e delineamento de blocos completos casualizados com três repetições. Foram avaliados o acúmulo total de forragem, o acúmulo de lâminas foliares, colmos e material morto, as variáveis morfogênicas e as estruturais, assim como a altura do dossel no pré-corte e a duração do período de rebrotação. O corte a 15 cm resultou em menor período de rebrotação, altura pré-corte, alongamento de colmo e tamanho final da folha e maior densidade populacional de perfilhos em comparação ao corte a 30 cm. O intervalo de corte correspondente ao aparecimento de cinco folhas por perfilho resultou em maiores alturas pré-corte, taxas de alongamento de folhas, tamanho final das folhas e acúmulo de colmos e em menor densidade populacional de perfilhos em comparação aos intervalos correspondentes a três e quatro folhas surgidas por perfilho. A maior eficiência de utilização dos pastos de capim-marandu foi alcançada com cortes a 15 cm. Pastos manejados com intervalo de corte correspondente a três folhas surgidas por perfilho, independentemente da altura de corte avaliada, acumulam elevada quantidade de folhas, componente altamente desejável para alimentação animal.

No abstract

Understanding of the morphogenetic characteristics allows comprehension of aspects related to the form and function of forage plants, providing opportunities to identify potentially high productive plants and distinct defoliation management requirements. The objective of this experiment was to carry out a comparative study of ten tropical forage grasses using morphogenetic and structural variables. Treatments corresponded to grasses of the Panicum genus (P. maximum cultivars Tanzânia and Mombaça) and the Brachiaria genus (B. brizantha cultivars Piatã, Marandu, Xaraés, Capiporã and Arapoty; B. decumbens cultivar Basilisk; B. humidicola cultivars Comum and Tupi), evaluated under free growth conditions.. Response variables were leaf appearance and elongation rates, phyllochron, stem elongation rate, final leaf length, number of live leaves per tiller, leaf life span and tiller appearance, death and survival rates. There was difference between cultivars for these variables, indicating a large variability within plants. Considering the morphogenetic and structural variables of leaves and tillers, B. brizantha had a similar pattern of variation to those of P. maximum, and B. Decumbens, similar to those of B. humidicola. Tiller appearance was large at the onset of the experiment and second and third generations comprised the large majority of tiller population for the cultivars Mombaça, Tanzânia, Xaraés and Capiporã. Group analysis based on plant morphogenetic and structural characteristics of leaves and tillers was an interesting way of grouping cultivars, indicating the importance and the potential of using morphogenesis in plant selection and evaluation programmes.

-This work was performed aiming to evaluate the morphogenetic and structural characteristics of Andropogon gayanus cv. Planaltina species submitted to three cutting heights (20, 27 and 34 cm). The three cutting heights were allocated in experimental units (12 m 2 ) in a complete randomized block design with three replications. The cuts were done when the light interception by the sward reached 95%. At this moment, the sward height revealed itself constant with values close to 50 cm. The lowest cutting height (20 cm) influenced negatively the final leaf blade length, the number of live leaves, the leaf lifespan, the stem elongation rate and the tiller population density, and it influenced positively the phyllochron and the leaf senescence rate. Probably, cuts at 20 cm height caused a high decapitation and death of the tillers. The worst growth conditions in addition to the blossom of this specie occurred during fall resulted in higher stem elongation rates and number of live leaves, and lower phyllochron, final leaf blade length, and leaf lifespan. The sward height can be used as a practical and efficient criterion in the management of andropogon grass. Under intermittent management conditions, the regrowth of andropogon grass must be interrupted when the sward reaches 50 cm height, and the defoliation must be interrupted when the stubble height is close to 27 cm.Key Words: Andropogon gayanus, ecophysiology, light interception, morphogenesis, sward height Características morfogênicas e estruturais do capim-andropógon submetido a diferentes alturas de corte RESUMO -Este trabalho foi realizado com o objetivo de avaliar as características morfogênicas e estruturais da espécieAndropogon gayanus cv. Planaltina, submetida a três alturas de corte (20, 27 e 34 cm). As três alturas de corte foram alocadas às unidades experimentais (12 m 2 ) em delineamento de blocos completos casualizados com três repetições. Os cortes foram realizados quando a interceptação luminosa pelo dossel atingiu 95%. A altura do dossel nesse momento mostrou-se constante, com valores próximos a 50 cm. A menor altura de corte (20 cm) influenciou negativamente o comprimento final da lâmina foliar, o número de folhas vivas, a duração de vida da folha, a taxa de alongamento de colmo e a densidade populacional de perfilhos, e positivamente o filocrono e a taxa de senescência de folhas. Provavelmente, cortes a 20 cm de altura causaram elevada decapitação e morte de perfilhos. As piores condições de crescimento junto do florescimento ocorrido durante o outono resultaram em maiores taxas de alongamento de colmos e número de folhas vivas e em menor filocrono, comprimento final da lâmina foliar e duração de vida da folha. A altura do dossel pode ser utilizada como critério prático e eficiente de manejo do capim-andropógon. Em condições de manejo intermitente, a rebrotação deve ser interrompida quando o dossel atingir 50 cm de altura, e a desfolhação, quando a altura de resíduo ficar próxima de 27 cm.

ABSTRACT. Current experiment identified the height of signal grass {Urochloa decumbens (Stapf) R. D. Webster cv. Basilisk [syn. Brachiaria decumbens Stapf cv. Basilisk]} at the beginning of deferment that provided an appropriate pasture structure and potential selectivity by cattle on deferred pastures. Four pasture heights at the beginning of deferment (10, 20, 30 and 40 cm) and two forage samples (available on pasture and simulated grazing) were studied. The experimental design was set in completely randomized blocks, with two replications, in a split-plot arrangement. Higher percentage of live leaf blades and lower percentage of live stems and senescent forage were recorded in the forage sample from simulated grazing. The increase in pasture height increased the percentage of senescent forage and reduced the percentage of live leaf blades in forage samples. Pasture height at the beginning of deferment did not affect the potential selectivity index by cattle for the percentage of live leaf blade. The potential selectivity index varied quadratically for the percentage of live stems and increased linearly for the percentage of senescent forage with pasture height. A 10-to-20 cm reduction in pasture height at the beginning of deferment improved the structure of deferred signal grass and optimized selectivity by cattle.Keywords: Brachiaria decumbens, stem, leaf, senescent forage, grazing.Altura do pasto no início do diferimento como determinante da estrutura do capimbraquiária e da seletividade potencial de bovinos RESUMO. Objetivou-se identificar a altura do capim-braquiarinha {Urochloa decumbens (Stapf) R. D. Webster cv. Basilisk [syn. Brachiaria decumbens Stapf cv. Basilisk]} no início do diferimento que possibilite adequada estrutura de pasto e seletividade potencial dos bovinos em pastagens diferidas. Foram estudadas quatro alturas do pasto no início do diferimento (10, 20, 30 e 40 cm) e duas amostras de forragem (disponível na pastagem e de pastejo simulado). O delineamento experimental foi em blocos completos casualizado com duas repetições, em esquema de parcela subdividida. Foi registrada maior porcentagem de lâmina foliar viva e menor de colmo vivo e forragem senescente na amostra de forragem em pastejo simulado. O incremento na altura do pasto aumentou o porcentual de forragem senescente e reduziu a porcentagem de lâmina foliar viva nas amostras de forragem. A altura do pasto no início do diferimento não influenciou o índice de seletividade potencial de bovinos para a porcentagem de lâmina foliar viva. O índice de seletividade potencial variou quadraticamente para a porcentagem de colmo vivo e aumentou linearmente para a porcentagem de forragem senescente com a altura do pasto. A redução da altura do pasto para 10 a 20 cm no início do diferimento melhora a estrutura do capim-braquiária diferido e otimiza a seletividade dos bovinos.Palavras-chave: Brachiaria decumbens, colmo, folha, forragem senescente, pastejo.

The study was carried out between March 1st and July 1st, 2011, in order to evaluate the tillering pattern of the deferred Piata palisade grass (Brachiaria brizantha cv. Piata). Three sward heights were evaluated in the beginning of the period of deferment: lower (20 cm), medium (30 cm) and higher (40 cm). The experimental design was of completely randomized blocks with three replications. The Piata palisade grass deferred with low initial height presented lower leaf area index, lower light interception and higher leaf angle in relation to the ones deferred with medium and high heights. The advance in the period of deferment increased the leaf area index and the light interception by the sward, in a way that the highest values were recorded in the periods from 91 and 120 days. The leaf angle reduced linearly with the advance in the period of deferment. For basal and aerial tillers, the rates of appearance, mortality and survival of tillers, as well as the balance between appearance and mortality, and the tiller density stability index were not affected by the initial height of the sward. The stability index of the tiller density was lower in the period from 1 to 30 days of deferment in relation to the periods from 31 to 60, from 61 to 90 and from 91 to 120 days. The variation of the initial height of the Piata palisade grass does not influence the tiller density dynamics during the period of deferment. The reduction of the initial height of the Piata palisade grass improves the luminous environment inside the sward, but it does not stimulate the grass tillering during the period of deferment.

The objective of this research was to assess morphogenetic and structural characteristics of tillers of guinea grass cv. Tanzania at different ages. The pastures of guinea grass were managed in six pasture conditions related to the combination of three frequencies (90, 95, and 99% light interception) and two post-grazing heights (25 and 50 cm). In these six pastures conditions, three tiller ages were evaluated (young, mature, and old). The design was of completely randomized block with three replications. Young tillers exhibited higher leaf appearance rate and leaf elongation rate and, consequently, higher final leaf length and number of live leaves than mature and old tillers, regardless of the pasture condition. On pastures managed with 90 or 95% light interception associated with a post-grazing height of 25 cm, old tillers presented longer leaf lifespan than young and mature ones. There is a progressive reduction in the vigor of growth of pastures of guinea grass cv. Tanzania with advancing tiller age

-This study was conducted in order to evaluate the morphogenetic and structural characteristics of guinea grass cv. Mombasa under three post-grazing heights (intense -30 cm, lenient -50 cm and variable -50 in springsummer and 30 cm in autumn-winter) when sward light interception reached 95% during regrowth. Post-grazing heights were allocated to experimental units (0.25 ha) in a completely randomized block design with three replications. Postgrazing heights affected only leaf elongation rate and the number of live leaves. Pastures managed with variable postgrazing height showed higher leaf elongation rate in the summer of 2007. This management strategy also resulted in a higher number of live leaves. During the spring of 2006, plants showed lower leaf elongation rate, leaf appearance rate and number of live leaves, and greater phyllochron and leaf lifespan. In contrast, during the summer of 2007, the leaf appearance rate, leaf elongation rate, number of live leaves, and final leaf length were greater while phyllochron, stem elongation rate, and leaf senescence rate were lower. The management of the guinea grass cv. Mombasa with intense or variable post-grazing height throughout the year seems to represent an interesting management target, in terms of leaf appearance rate and number of live leaves.