Estudo do desempenho animal e produção do capim Tanzânia (Panicum maximum, Jacq.) em um sistema rotacionado de pastejo sob irrigação em três níveis de resíduo pós-pastejo. / Study of the animal performance and herbage production of irrigated tanzania grass (Panicum maximum, Jacq.) in a rotational grazing system under three post-grazing residues levels.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

This research was to evaluate effect of the post-grazing pasture mass on morphological characteristics, herbage production and animal performance and productivity from irrigated and rotationally grazed system with Panicum maximum Jacq. cv. Tanzânia. The experimental period was October 30/1999 to January 03/2001 and established at Escola Superior de Agricultura "Luiz de Queiroz", Piracicaba/SP. A complete randomized block design with three postgrazing residues (1.000, 2.500 e 4.000 kg/ha of green dry matter - GDM) and four replicates was used. The grass seeding was performed on March 17/1999 and soil was limed and fertilized to 80% base saturation, phosphorus (resin) level of 30 mg/cm3 and 5% potassium in the cation exchange capacity. In each grazing cycle paddocks were fertilized with 24-04-24 (334 kg/ha). Nellore steers with approximately 10 months of age were used. Four pre-experiments were conducted, the first three to determine the best dimesion:format ratio of the sampling unit and the most appropriate number of samplings in evaluating herbage mass. The fourth pre-experiment aimed to evaluate the relationship between grazing depth (progressive sward defoliation during the grazing period) and plant height before grazing. Herbage mass evaluation in tussock-forming pastures should be performed taking four 1 m2 samples (1m x 1m). Grazing depth was linearly correlated to plant height, irrespective of grazing intensity and days on the grazing period. Grazing intensity had no effect on the slope of the angle between soil and tillers on the border of the tussock, neither on tussock shape nor on forage bulk density across the sward profile, indicating Tanzania grass has limited plasticity for these characteristics. However, stem, leaf and dead material proportion in herbage samples, as well as leaf/stem ratio and plant height were affected by treatments (post-grazing residues) and season of the year. The ground area covered by grass tussocks decreased during the experimental period, irrespective of the treatment. The tussock size was associated with fast adaptation mechanisms of the plants in response to changes in environment resulting from different post-grazing herbage masses. Animal performance was better related to herbage allowance and post-grazing residues than with leaf/stem ratio or forage bulk density. Treatments did not altered animal productivity. In spite of this, it would be more adequate to allow post-grazing pasture mass to be higher than 2.915 kg GDM/ha and herbage allowance to be higher than 14,9 kg GDM/100 kg live weight (LW) or 6,1 kg of leaves/100 kg LW. This grazing management would improve animal performance and anticipate slaughter age in 150 days when compared to the treatment with post-grazing pasture mass of 1.266 kg GDM/ha.

ASSUNTO(S)

cattle forragem animal growth desempenho animal panicum maximun produtividade animal capim colonião pastures rotational grazing bovino animal productivity pastejo rotativo

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