Carlos Guilherme Silveira Pedreira

Respostas morfológicas do capim-Tanzânia (Panicum maximum Jacq. cv. Tanzânia-1) irrigado à intensidade de desfolha sob lotação rotacionada

Objetivando quantificar respostas morfologicas de dosseis de capim-Tanzânia (Panicum maximum Jacq. cv. Tanzânia-1) sob tres intensidades de pastejo, lotacao rotacionada e irrigacao, foi conduzido um experimento em delineamento experimental de blocos completos casualizados com quatro repeticoes. Os tratamentos foram tres intensidades de pastejo, representados pelas quantidades de massa seca verde residual pos-pastejo (T1=1000; T2=2500 e T3=4000 kg MSV/ha). Durante oito ciclos de pastejo (rebrotas de 33 dias apos tres dias de pastejo em cada ciclo), foram realizadas avaliacoes de altura media do dossel, indice de area foliar (IAF), interceptacao luminosa (IL) e ângulos foliares medios, em quatro dias dentro do periodo de rebrota (1, 11, 22 e 33 dias apos a saida dos animais). A analise de correlacoes parciais indicou correlacoes entre altura e IL, bem como entre IAF e IL. Com o progresso da estacao de pastejo, da primavera-verao para outono-inverno, houve reducoes nos valores de IAF medio. Valores medios de IAF critico (95% IL) de 3,6 (T1), 4,0 (T2) e 4,5 (T3), foram alcancados por volta do 22o dia das rebrotas. A maior intensidade de pastejo (menor residuo) alterou a estrutura da pastagem no que diz respeito a arquitetura do dossel, evidenciada pela reducao nos ângulos foliares medios (folhas mais horizontais) ao longo das estacoes, com plantas passando a interceptar mais luz por unidade de area foliar. Os IAFs criticos medidos sugerem a necessidade de periodos de descanso menores que 33 dias em pastos de capim-Tanzânia, quando submetido a pastejo intensivo sob lotacao rotacionada e irrigacao.

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.

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.

Fotossíntese foliar do capim-xaraés [Brachiaria brizantha (A. Rich.) Stapf. cv. Xaraés] e modelagem da assimilação potencial de dosséis sob estratégias de pastejo rotativo

The objective of this research was to quantify leaf photosynthetic rates during the regrowth period and to model canopy photosynthesis of vegetative swards of Xaraes palisadegrass [Brachiaria brizantha (A. Rich.) Stapf.] under contrasting management strategies of rotational stocking. Early regrowth was characterized by low photosynthetic potential (10.4 µmol CO2 m-2 s-1) and for paddocks under the 100% LI treatment, leaf photosynthesis was 3.3 µmol CO2 m-2 s-1, which may require plants to draw on organic reserves during the early phases of the process. Half way through regrowth, leaf photosynthetic rates increased to 26 µmol CO2 m-2 s-1 in all treatments. Paddocks under the 95% LI treatment (shortest mean regrowth periods; 22 days), sustained pre-graze photosynthetic rates at 26.1 µmol CO2 m-2 s-1. The longer regrowth intervals (28 and 32 days on average, for the 28 d and for the 100% LI paddocks, respectively), resulted in lower rates of 21.3 and 24.5 µmol CO2 m-2 s-1, respectively. Under the highest grazing frequency (95% LI), the short rest period and the low mean LAI (2.08) allowed for more light penetration into the canopy. Optimum management practices for Xaraes palisadegrass should include grazing intervals shorter than 28 days, so that higher photosynthetic rates are achieved during the regrowth period.

Desenvolvimento de modelos preditores de acúmulo de forragem em pastagens tropicais

The objective of this work was to identify, quantify and model conditioning attributes of forage accumulation in Central Brazil, and to develop estimating models of the forage accumulation potential, based on climatic parameters. A database structure was modeled and implemented for forage growth data insertion. Primary data experiments with Cynodon, Panicum and Urochloa cultivars were inserted. The databank allowed the generation of sorted lists of forage mean accumulation rates (TMA), average temperature, maximum and minimum (Tmin) temperatures, global incident radiation and day of the year, for each growth period. Simple and multiple linear regressions were made, with climatic variables as regressors and TMA as response variable. The model with Tmin as independent variable was adopted as standard because it stood out for the best values of determination coefficient, Akaike criterion and Bayesian criterion. The models were grouped by the coincidence test in six groups. The models have different estimating capacities for each cultivar. Model calibration using local data can accommodate effects disregarded in its formulation, and enhances potential yield estimative accuracy.

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.

Eficiência de pastejo de capim-marandu submetido a diferentes ofertas de forragem

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.