Sila Carneiro da Silva

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.

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.

Avanços na pesquisa com plantas forrageiras tropicais em pastagens: características morfofisiológicas e manejo do pastejo

Grazing management has been the focus of the research with forage plants in Brazil for many years. However, it was during the last decade that significant changes and advance occurred regarding the understanding of important factors and processes that determine adequate use of tropical forage plants in pastures. The objective of this text is to provide a brief history of the research on forage plants and grasslands in Brazil, highlighting its evolution, trends, results and transition phases. That will help to put things into perspective and provide the basis for discussing the importance and relevance of studies involving evaluations of morphophysiological traits and responses of forage plants towards planning and definition of sound and efficient grazing management practices. The information is presented in a systematic manner, favouring an integrated view of the different trends and research philosophies used, indicating, critically, the need for revising and changing paradigms as a means of improving and consolidating the knowledge on animal production from pastures.

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.

Acúmulo de forragem durante a rebrotação de capim-xaraés submetido a três estratégias de desfolhação

The objective of this research was to describe comparatively the dynamics of herbage accumulation in Xaraes palisadegrass pastures [Brachiaria brizantha (A. Rich.) Stapf cv. Xaraes] submitted to rotational stocking managements, defined either by pre-graze light interception (LI) by the canopy (95% or 100% LI) or calendar days (28d). Pre-graze forage mass (FM) was higher for 100% LI pastures. Pastures grazed at 95% LI and 28-d resulted in similar pre-graze FM in the spring, both lower than that of the 100%-LI treatment. Grazing at 95% LI resulted in higher leaf percentage in pre-graze forage, although total pre-graze FM was lower. Forage produced in paddocks grazed at 100% LI had lower pre-graze leaf percentage, indicating that the higher forage accumulation in that treatment was a result of higher stem elongation, likely due to light competition within the canopy. Rest periods beyond the point where swards achieved 95% LI (100% LI or 28-d during the summer) resulted in higher accumulation and higher pre-graze FM, although this corresponded mainly to large amounts of stem and dead material, which could negatively affect the nutritive value of the forage produced and animal performance.

Ingestive behaviour, herbage intake and grazing efficiency of beef cattle steers on Tanzania guineagrass subjected to rotational stocking managements

The objective of this experiment was to evaluate the ingestive behaviour, herbage intake and grazing efficiency of beef cattle steers grazing on Panicum maximum Jacq. cv. Tanzania subjected to different rotational stocking intensities. Treatments corresponded to two post-grazing conditions (residues of 25 and 50 cm) associated with a pre-grazing condition of 95% sward canopy light interception during regrowth (LI). The grazing time increased linearly with the duration of the occupation period (475 to 630 minutes/day). On paddocks grazed down to a residue of 25 cm, the bite rate increased linearly along the occupation period, with an average of 42.5 bites/minute. On paddocks grazed down to a residue of 50 cm, the bite rate was stable and equal to 39 bites/minute. There was no difference in herbage intake between grazing intensities. However, grazing at 25 cm residue resulted in greater herbage removal (68.0 vs. 45.6%) and greater grazing efficiency (90.4 vs. 49.8%) than grazing at 50 cm residue. Post-grazing residues of Tanzania guineagrass under rotational stocking management may be set at either 25 or 50 cm, since the herbage intake was not affected within this grazing intensity range. However, herbage removal and grazing efficiency were reduced with the 50 cm post-grazing height and grazing time increased with long occupation periods.

Características do processo de ingestão de forragem por novilhas holandesas em pastagens de capim-mombaça

Para avaliacao da influencia da estrutura do dossel de pastagens tropicais sobre o processo de ingestao de forragem por bovinos, cinco alturas de dossel (60, 80, 100, 120 e 140 cm) de uma pastagem de capim-mombaca (Panicum maximum, Jacq.) foram estabelecidas, em um delineamento inteiramente casualizado, com duas repeticoes. Quatro novilhas da raca Holandes Preto e Branco com coletores de fezes e urina foram utilizadas em testes de pastejo de 45 minutos. O numero de bocados e o tempo de alimentacao foram registrados com o uso de contadores e cronometros. A massa de forragem total consumida foi obtida pela tecnica de dupla pesagem. Com o aumento na altura do dossel, observou-se aumento linear na massa de bocado. O aumento do comprimento das lâminas foliares expandidas e em expansao resultou em consumo quase que individual de folhas, refletindo em aumento linear no tempo por bocado e em reducao linear na taxa de bocados. Uma vez que o aumento no tempo por bocado foi proporcionalmente maior que o aumento da massa de bocado, a massa de forragem total consumida e a taxa de ingestao estabilizaram-se nas maiores alturas da pastagem. As limitacoes fisicas impostas pela estrutura do dossel levaram a menor eficiencia de captura de forragem pelos animais nas maiores alturas do dossel. O consumo de forragem foi maximizado a altura de 109,3 cm.

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

Características morfogênicas e estruturais e produção de forragem do capim-marandu submetido a intensidades e freqüências de desfolhação

This trial was carried out to evaluate the influence of defoliation intensities (10 and 20 cm stubble height) and defoliation frequencies (three cut intervals based on the appearance of 5, 7 and 9 leaves/tiller after each defoliation event) on the morphogenetic and structural traits, tillering and herbage production of Brachiaria brizantha cv Marandu swards. Treatments were allocated to experimental units according to a completely randomized design, in a 2 x 3 factorial arrangement, with three replications, in a total of 18 experimental units. Two cuts were performed in the most frequent treatment and one cut for the remaining treatments. Greater defoliation intensity resulted in greater leaf tissue turn over and, when combined to greater defoliation frequencies resulted in younger tillers, which grew up in an environment with lesser light competition. Cutting intensity at 20 cm favored tiller transition from vegetative to reproductive stage, resulting in greater contribution of pseudo stem and dead material to the herbage mass. If frequent defoliation is used, the 10 cm stubble height is the recommended intensity. If less frequent defoliation is used, the 10 cm stubble height may decrease herbage yield, mainly when using the seven leaves frequency. Greater defoliation frequencies showed greater sward renovation, with greater leaf elongation and leaf appearance rates, greater leaf blade length and lesser pseudo-stem accumulation and elongation. Although greater herbage production was obtained at the 20 cm cutting height and 7 leaves frequency, considering all evaluated traits, more frequent cuts promoted greater tissue turn over with high herbage production characterized by its high amount of leaves and less amount of pseudo stem and dead material, allowing for higher herbage production efficiency.

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.