Adubação nitrogenada de capins tropicais : momento de aplicação e digestão in vitro da forragem

Abstract

Due to the need to adopt adequate management practices in pasture animal production systems, the objective was to define the most appropriate time for nitrogen fertilization of Urochloa brizantha cv. Piatã and Panicum maximum cv. Quênia, and to verify if nitrogen fertilization, when associated with supplements, influences the in vitro digestion of Urochloa brizantha cv. Marandu. Two experiments were carried out in this study. The first occurred in a greenhouse, using a completely randomized design, with ten replications. The treatments consisted of five moments of nitrogen fertilization (0, 2, 4, 6 and 8 days after defoliation), for the Piatã Palisadegrass and Quênia Guineagrass. The evaluated productive characteristics were: dry mass of the leaf blade, stem + sheath, residue and roots, and the content of the forage root system non-structural carbohydrate was quantified. In the second experiment, with Marandu Palisadegrass, the experimental design was completely randomized, with four replications. The treatments were arranged in a 5 x 3 factorial scheme, with five doses of Nitrogen (0; 25; 50; 75 and 100 kg ha-1 cut-1), and three associations with supplement (without supplement; protein supplement and energy supplement). The fermentation kinetics and in vitro dry matter digestibility were evaluated. In the results obtained from the first experiment there was a reduction of 39% in the dry mass of the leaf blade of Piatã Palisadegrass when fertilized eight days after cutting, in relation to fertilization at the moment of defoliation. It is concluded that the Piatã Palisadegrass has a high initial requirement after defoliation, and it is recommended to apply Nitrogen as close as possible to the cut. For Quênia Guineagrass, nitrogen fertilization can be carried out between the day of defoliation and the eighth day after, without significant changes in production. Regarding root analysis, the timing of application of Nitrogen causes variations in the levels of non- structural carbohydrates of the evaluated forages. In the second experiment it is concluded that increasing doses of nitrogen fertilization reduce the in vitro digestibility and fermentation gas volume of the Marandu Palisadegrass. The addition of supplements increased (p < 0.05) the forage digestibility, and the energy supplement provided an increase of 10% in this variable. Supplementation is an option that can improve the nutritive value of the diet of animals grazing in pasture of Marandu Palisadegrass fertilized with Nitrogen, during the water season.