Capim-Piatã (Urochloa brizantha cv. Piatã) manejado sob lotação intermitente em função da altura do pasto por bovinos na Amazônia Legal.

Abstract

Knowledge of plant responses submitted forage grazing frequencies is important to generate information about the soil-plant-animal determinant of livestock. The research objective was to evaluate the relationship at the interface soil-plant-animal in Piatã-Grass grazing at different heights in the canopy entry (30, 40 and 50 cm) under intermittent stocking with variable stocking rate. To evaluate the morphogenesis the experimental design was a randomized block in split-plot at time, with three treatments and four replications over three growing seasons. While, for agronomic and chemical characteristics of forage was completely randomized with three treatments and four replications for characteristics related to the evaluation of pastures and grazing cycles Feeding behavior and pattern of movement of animals were evaluated a randomized block in split plot, the heights consisting the main plots and the condition (input and output) the sub-plots. The pastures of Piatã-Grass responded heights, increasing SER, SLR, FILO and IRFA, decreasing LER and DPP pair the greatest heights of entry, in part due to the change in the period of rest the pastures to reach the desired heights. Most of the features that make up the herbage mass and structure of the pastures of Piatã-Grass were sensitive input heights and grazing periods, especially in a condition of entry. In general, the leaf/stem ratio and leaf area index remained stable from the height of 40 cm, with the same response pattern over the course of the grazing season. The heights of the entrance canopy did not affect (P>0.05) time grazing, ruminating and resting, but significant effect to the structural condition, and in the early morning and late afternoon, almost all the time was used the grazing activity. Shorter grazing (P< 0.05) was recorded (379.4 min) and the input condition to the larger displacement 50 cm (7.7 steps/min). The input condition resulted in a canopy structure that increased the speed of forage intake with lower input time per meal (56.7 min) relative to the outlet (74 min). Bite rate and the number of bits per season have changed the heights, with greater value for the pastures of 30 cm (38.9 bits/min and 8.2 bits/season, respectively). Significant variation (P<0.05) for dry matter (DM), total dry matter output (DMToutput) and root dry mass (DMR), with higher values for higher pastures managed. The relationship MSPA/DMR and % root colonized (%RC) were not affected by heights with a mean value of 1.2 ± 0.14 and 55%, respectively. The increase in the regrowth period negatively affected the structure of the canopy, reducing the levels of N and K for longer intervals of regrowth over the grazing season. Higher values of extraction of N= 112.2, P= 7.9 and K= 88.9 kg/ha/cycle were for the most entry height in the canopy. The Piatã-Grass must be maintained between pre-grazing heights of 30 and 40 cm. The extension of the period of rest beyond this range dramatically alters the morphogenesis, raising the SER and LSR, undesirable in cattle grazing because normally depress forage intake. It was evident the greater forage availability (input condition relative to output), less time is allocated to grazing activity and increased the number of short meals accompanied by long intervals between meals. And the smaller the forage mass, even with higher nutritional value, the lower the accumulation of nutrients snapshot. However, the greater the number of cycles grazing 30 and 40 cm reflected in higher extraction efficiency of N and using the N, P and K.