Roberta Aparecida Carnevalli

Sward structural characteristics and herbage accumulation of Panicum maximum cv. Mombaça subjected to rotational stocking managements

Grazing strategies promote changes in sward structure that can affect patterns of herbage accumulation and sward flexibility to management. This experiment evaluated sward structural characteristics and herbage accumulation of Mombaca guinea grass (Panicum maximum Jacq. cv. Mombaca) subjected to rotational stocking managements. Treatments involved grazing when swards reached either 95 or 100% interception of the incident light (LI), to post-grazing heights of 30 and 50 cm, and were allocated to 2,000 m2 paddocks according to a randomised complete block design in a 2 × 2 factorial arrangement with four replications, from January 2001 to February 2002. Sward canopy changed from a vertical to a more horizontal orientation as the light interception area index and height increased from post to pre-grazing. Leaf canopy height pre-grazing was stable throughout the year and around 90 and 115 cm for the 95% and 100% LI treatments respectively, indicating a potential for development and use of target-based grazing management practices. Herbage mass pre and post-grazing was lower for the 95% than the 100% LI treatments, but with higher proportion of leaf and lower proportions of stem and dead material. Treatment effects on herbage accumulation were cumulative and became more evident as the experiment progressed, with up to 6 t ha-1 DM advantage to the 95/30 treatment. Although based on a single year experiment, grazing management should aim for low herbage mass during the transition period from winter to spring in order to allow fast recovery of swards and favour herbage accumulation during the following growing season.

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.

VALIDAÇÃO DE TÉCNICAS EXPERIMENTAIS PARA AVALIAÇÃO DE CARACTERÍSTICAS AGRONÔMICAS E ECOLÓGICAS DE PASTAGENS DE CYNODON DACTYLON CV. 'COASTCROSS-1

Este trabalho consiste na avaliacao de uma pastagem tropical Cynodon dactylon, enfocando, principalmente necessidade de adaptacao, afericao da precisao e transferencia de metodologias comumente utilizadas para plantas de clima temperado. Neste estudo, pode-se avaliar producao de forragem, composicao botânica, crescimento por perfilho e senescencia foliar (fluxo e renovacao de tecidos) e dinâmica populacional de perfilhos (morte, sobrevivencia e aparecimento de perfilhos), relacionada com a densidade de perfilhos (numeros de perfilhos/m2), possibilitando a deteccao de falhas e imprecisoes nestes metodos quando transferidos de forma direta de comunidades de plantas de clima temperado para plantas de clima tropical. Foram geradas, ainda, equacoes de calibracao, ou seja, relacao entre altura e massa de forragem do pasto, as quais sofreram modificacoes ao longo do ano devido a mudancas, principalmente, na estrutura do pasto.

Índice de área foliar, coeficiente de extinção luminosa e acúmulo de forragem em pastagens de Cynodon spp. sob lotação contínua

Leaf area index, light extinction coefficient and herbage accumulation were evaluated in three Cynodon spp. cultivars (Tifton85, Florakirk and Coastcross) submitted to four grazing intensities (5, 10, 15 and 20cm) imposed by sheep under a continuous stocking management. The experimental design was a complete randomized blocks with four replications, with treatments in a split plot arrangement. Grass cultivars were allocated to plots and grazing intensities to subplots. The largest values of LAI were observed for Tifton85. Light extinction in the sward was a function of grass cultivar, time of the year and phenological state of pasture plants. Florakirk presented the highest values of light extinction coefficient (k), but k was higher for lower grazing intensities. No differences were observed in herbage accumulation rates among the grass plants studied.