André Fischer Sbrissia

Compensação tamanho/densidade populacional de perfilhos em pastos de capim-marandu

Este trabalho foi realizado para verificar a existencia de relacao entre tamanho e numero de perfilhos em pastos de capim-marandu e testar se ajustes relacionados a variacoes em indice de area foliar (IAF), relacao area foliar:volume por perfilho (R) e densidade aparente de perfilhos na equacao de predicao da resposta permitiriam explicar eventuais desvios da inclinacao teorica predita. Foram avaliadas quatro condicoes da pastos (10, 20, 30 e 40 cm de altura), mantidas constantes por bovinos em regime de lotacao continua e taxa de lotacao variavel. O delineamento experimental foi o de blocos completos casualizados com quatro repeticoes. Avaliaram-se a densidade populacional de perfilhos, a massa por perfilho, a area foliar por perfilho, o indice de area foliar, a relacao folha/colmo e a razao area foliar:volume do perfilho (R). Alem disso, regressoes lineares simples foram realizadas para a avaliacao dos parâmetros da relacao funcional entre densidade populacional e massa por perfilho. As medicoes foram realizadas de janeiro a dezembro de 2002. Pastos de capim-marandu possuem um mecanismo de compensacao tamanho/densidade populacional de perfilhos pelo qual maiores densidades populacionais estao associadas a perfilhos pequenos e vice-versa. Os valores de R apresentaram variacoes sazonais, indicando que perfilhos desta especie podem reduzir area foliar em relacao ao seu volume como mecanismo de sobrevivencia em condicoes de deficit hidrico. As analises de regressao revelaram coeficientes lineares menores que -3/2, de modo que os desvios desta expectativa foram explicados pelas variacoes registradas em IAF, R e na densidade aparente de perfilhos.

Tiller size/density compensation in grazed Tifton 85 bermudagrass swards (1)

(3) Abstract - The objective of this study was to evaluate the occurrence of the tiller size/density compensation mechanism in Tifton 85 bermudagrass swards grazed by sheep under continuous stocking. Treatments corresponded to four sward steady state conditions (5, 10, 15, and 20 cm of sward surface height), maintained by sheep grazing. The experimental design was a complete randomized block with four replicates. Pasture responses evaluated include: tiller population density, tiller mass, leaf mass and leaf area per tiller, and herbage mass. Tiller volume, leaf area index, tiller leaf/stem ratio, and tiller leaf area/volume ratio were calculated and simple regression analyses between tiller population density and tiller mass were performed. Measurements were made in December, 1998, and January, April, and July, 1999. The swards showed a tiller size/density compensation mechanism in which high tiller population densities were associated with small tillers and vice-versa, except in July, 1999. Regression analyses revealed that linear coefficients were steeper than the theoretical expectation of -3/2. Increments in herbage mass were attributable to increases in tiller mass in December and January. Leaf area/volume ratio values of Tifton 85 tillers were much lower than those commonly found for temperate grass species.

Desempenho de ovinos e respostas de pastagens de tifton 85 (Cynodon spp.) sob lotação contínua

ABSTRACT: The use of pastures for feeding ruminants is increasing in recent years due to its low cost comparativelyto other sources of feed. In that sense, forage plants with good performance under grazing and presenting highflexibility of utilisation have raised a great deal of interest. In this context, pasture and animal performance wereevaluated on Cynodon spp. (cultivar Tifton 85) swards kept in four steady state conditions (50, 100, 150 and 200 mmsward surface heights - SSH) with sheep grazing under continuous stocking and variable stocking rate from august/1998 to april/1999. Treatments corresponded to the SSH and were allocated to experimental units according to acomplete randomised block design with four replications. Individual experimental units (400 2 each) were grazed,mat least, by two lambs to estimate animal responses, with three exclosure cages for herbage accumulationmeasurements. Experimental responses evaluated were: crude protein (CP), neutral detergent fiber, acid detergentfiber and lignin, and

Dry matter accumulation dynamics in grazed Tifton 85 bermudagrass swards

Herbage dry matter accumulation from forage plants results from the balance between growth and senescence. Agronomic practices may influence both processes in different ways and, therefore, alter the quantitative and qualitative patterns of dry matter production. This study aimed at evaluating the process of dry matter accumulation through measurements of growth and senescence. Experimental treatments corresponded to four sward state conditions (5, 10, 15 and 20 cm of sward surface height - SSH) generated by sheep grazing under continuous stocking and variable stocking rate. The experimental design was a complete randomised block, with four treatments and four replicates. Pasture responses evaluated were: stem elongation, leaf lamina elongation, senescence, phyllochron and number of leaves per tiller. The results showed a seasonal pattern of herbage production with the highest growth and senescence rates observed at the highest SSH studied (15 and 20 cm). Phyllochron varied according to time of the year and SSH, revealing an intimate relationship with air temperature variation, soil water availability and sward leaf area index. SSH of 15 and 20 cm resulted in the highest dry matter production. The same principles and relationships originally described for herbage accumulation in temperate grass pasture species are valid for tropical areas within the framework of the physiological and environmental constraints inherent to each condition.

Índice de área foliar, interceptação luminosa e acúmulo de forragem em pastagens de Cynodon spp. sob diferentes intensidades de pastejo

Leaf area index (LAI), light interception and herbage accumulation were evaluated for three Cynodon spp. cultivars (Tifton-85, Florakirk and Coastcross) submitted to four grazing intensities (5, 10, 15 and 20 cm) established by sheep under a continuous stocking management. A complete randomised block design was used with four replications, with treatements in a split-plot arrangement. Grass cultivars were allocated to plots and grazing intensities to sub-plots. The largest values of LAI were observed for Tifton-85. Rates of dry matter accumulation were similar for all treatments. Tifton-85 presented a narrower optimal range for pasture conditions (5 to 15 cm) as compared to Florakirk (5-20 cm) and Coastcross (5-20+ cm). Different grass cultivars presented different grazing management requirements in situations where the efficient use of light and high levels of herbage utilisation were targeted.

Morphogenetic and structural comparative characterization of tropical forage grass cultivars under free growth

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 Mombaca) and the Brachiaria genus (B. brizantha cultivars Piata, Marandu, Xaraes, Capipora 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 Mombaca, Tanzânia, Xaraes and Capipora. 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.

Morphogenetic and structural characteristics of xaraes palisadegrass submitted to cutting heights

The objective of this work was to evaluate the morphogenetic and structural characteristics of xaraes palisadegrass submitted to three cutting heights (15, 20 and 25 cm) when the sward reached 95% of light interception during regrowth. The experiment was carried out according to a complete randomized block design with three replications. The sward surface height under the cutting condition of 95% of light interception was very homogeneous with values around 30 cm. The increase in cutting height reduced the leaf elongation rate and the number of live leaves but increased stem elongation rate. As the cutting criterion was the same, before the intense competition for light, the variation in the cutting severity had a small influence on the morphogenetic and structural characteristics of this grass. In the summer, due to the better growth conditions, the plants presented a higher tissue renewal, which was characterized by a higher leaf elongation rate, reduced leaf lifespan and leaf senescence rate when compared to the other season of the year. Under intermittent defoliation conditions, the regrowth of xaraes palisadegrass can be interrupted at a sward height of 30 cm (frequency) keeping a residual height of 15 cm.

Distribuição de colmo na estrutura vertical de pastos de capim Aruana e azevém anual submetidos a pastejo intermitente por ovinos

The aim of this study was to determine the relative contribution of stem in the vertical structure of Aruana guineagrass and annual ryegrass pastures submitted to strategies of rotational grazing by sheep. Treatments for Aruana guineagrass corresponded to grazing when the swards intercepted 95 and 98% of the incident light (LI) until the post-grazing heights of 10 and 15cm. For annual ryegrass, treatments corresponded to grazing when the swards reached 15 and 25cm (pre-grazing heights) until the post-grazing of 4 and 8cm. The experimental design for two species was a completely randomized in a 2x2 factorial scheme, with three replications. To quantify the stem mass present at each 5cm in the vertical structure of the pastures two samples were taken per experimental unit (paddocks of 196m2) using a square of 25cmx25cm. Cut samples was separated in leaves, stem and dead material. Regardless of plant species or pre-grazing height, approximately 90% of the stem is present up to 50% of sward height, suggesting that reported intake reduction beyond this point can be attributed to difficulties in forage manipulation and apprehension.

Morphogenetic and structural characteristics of andropogon grass submitted to different cutting heights

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 m2) 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.

Frequencies and intensities of defoliation in Aruana Guineagrass swards: accumulation and morphological composition of forage

The objective of this study was to assess the accumulation and morphological composition of forage in Aruana Guineagrass (Panicum maximum cv. Aruana) swards subjected to intermittent stocking with sheep. Experimental treatments when grazing was introduced included low (95%) and high (98%) incident light interception and low (10 cm)- and high (15 cm)-residue height and were allocated to experimental units (196 m2 fenced areas) in a completely randomized 2 × 2 factorial arrangement with three replicates. Treatments were imposed between January and May 2009. More frequent grazing cycles (95% light interception) resulted in better control of stem elongation, lower proportion of dead plant material and invasive plants, and higher proportions of leaf blades in the grazing strata, compared with less frequent grazing cycles (98% light interception). Grass managed with 95% light interception combined with 10 and 15 cm post-grazing height and grass managed at 98% light interception combined with 15 cm post-grazing height did not show differences in forage accumulation rate. These results indicate that more frequent (30 cm pre-grazing height) and less severe (15 cm post-grazing height) grazing cycles provided animals with high leaf blade mass and low stem mass forage.