Intensidade de desfolhação orientada pelo resíduo de lâmina foliar no pós-pastejo de bovinos em capim-Piatã.

Abstract

The objective of this study was to evaluate the management of the Urochloa brizantha cv. Piatã grass. Two tests were performed for the evaluation. The first test consisted in monitoring the evolution of the Piatã grass during 49 days, by the evaluating of tillering, forage biomass, leaf area index (IAF), interception of photosynthetically active radiation (IRFA), relative growth rate (TCR), and net assimilation rate (TAL). The pasture was fertilized with 40 and 80 kg ha-1 of nitrogen and potassium, respectively. The second test was to evaluate the termination of beef cattle managed in intermittent system, with entry height fixed (35 to 40 cm), and the moment of exit determined by three residues of leaf blade (2, 4 and 6 cm). Morphogenic and structural characteristics were monitored during two growing seasons (rainy and drought-rainy), and the agronomic and chemical characteristics of the forage were studied during five grazing cycles, using 18 animals. These animals were managed in 4.8 ha of Piatã grass divided in six modules with four pickets of 0.2 ha. The ingestive behavior and the displacement pattern of the animals were evaluated in two conditions (entry and exit of animals). The height of the canopy showed linear growth, reaching 70.25 cm at 49 days in the highest fertilization. The tillering decreased in the last three weeks. IRFA evolved asymptotically, with maximum values of 94% in both fertilizations. TCR and TAL showed decreasing asymptotic evolution, because of the high proportion of stem in the canopy, during the 49 days. The morphogenic characteristics were not influenced by the treatments and seasons, which promoted little change in the structural characteristics, only in the mean sheath length (CMB) in the season and population density of tiller (DPP). The highest value found for CMB, at the rainy station 210.37 mm versus 175.89 mm, for the transition (drought-rainy). DPP presented the lowest value (680 tiller m-2 ) with the largest removal (2 cm). The residue of leaf blade had little effect on animal behavior, being more influenced by the conditions of the pasture, entry and exit of animals. This result was found, because the greater forage mass at the entry, the animals reduced grazing time, time per meal, number of bites, total number of morsels, total number of seasons, total number of steps, and increased the duration time of meal interval, in addition to the time per food season. Animal performance was directly influenced by RLF, with a lower daily mean gain (ADG) at 2 cm (0.575 kg animal-1 day-1 ) and higher at 6 cm (0.753 kg animal-1 day-1 ). In part, this fact was associated to the greater displacement of the animals in pastures with greater intensity of exit. However, the lowest weight gain was compensated by the higher stocking rate (TL) for this strategy (6.60 UA), in relation to the one with the highest residue of leaf blade post-grazing (5.32 AU), which maintained the constant weight gain per area (615.30 kg ha-1 ), for the managements. Fertilization changes the window of management of the Piatã grass, which can be managed with the three evaluated post-grazing strategies (2, 4 and 6 cm), provided that the rest period be variable, respecting the plant growth.