Avaliação agronômica, índices de vegetação, percentual de cobertura do solo e composição bromatológica do capim piatã sob pastejo e fertilização nitrogenada

• Autor(a) principal: Farias, Lorraine do Nascimento
• Data de Publicação: 2019
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da UFMT
• Texto Completo: http://ri.ufmt.br/handle/1/5040
• topic: Acúmulo de forragem; Eficiência de utilização do nitrogênio; Morfogênese; Nitrogênio; CNPQ::CIENCIAS BIOLOGICAS; Forage accumulation; Nitrogen utilization efficiency; Morphogenesis; Nitrogen

The objective was to evaluate the morphogenic, structural, accumulation, forage production and efficiency of nitrogen utilization, chemical composition, vegetation indexes and percentage of soil cover of pastures of pasture grass under grazing and nitrogen fertilization. The experiment was carried out in the forage field of the Animal Science course of the Federal University of Mato Grosso, in a randomized block design with four treatments (0, 150, 300 and 450 kg of N/ha/year) and three replications, in plots of 36 m2 . The grazing was carried out with sheep when the forage canopy reached 95% light interception (IL) up to 20 cm post-grazing. Nitrogen fertilization was applied in installments, according to the treatments. The management of grazing with intermittent stocking was characterized by the entry and removal of the animals from the plots under the condition that the pasture presented light interception (IL) of 95% of active photosynthetic radiation (pre-grazing) and 20 cm of height (post grazing) , respectively. The studied forage species was Brachiaria brizantha cultivar BRS piatã. A complete randomized complete block design was used in a split plot arrangement with three replications. The main plots were the applications of 0, 150, 300 and 450 kg ha of N in the form of urea, and the subplots were the seasons of the year: late summer / fall, winter, spring and summer. Experiment 1: The evaluation of the morphogenetic and structural characteristics was performed in seven tillers per experimental unit. After each grazing cycle, the tillers were randomly marked at points representative of the average pasture condition (by visual evaluation of height and forage mass). Each three tillers were evaluated and measurements were taken from the lengths of leaf blade and stem (stem + leaf sheath), leaf appearance, leaf expansion and senescence. Nitrogen fertilization positively affects the morphogenic and structural characteristics of the grassy piatã under rotational stocking. This effect can be optimized during rainy periods in the spring and late summer / fall. Experiment 2: Plant biomass samples were collected from pre-grazing and postgrazing conditions in two 0.25 m2 (0.70 x 0.35 cm) metal frames per picket, positioned at random points representative of the average pasture height, obtained through visual evaluation. The accumulation of dry mass of forage, stem, leaf blade and dead tissue in kg ha-1 was obtained by the difference between the pre-grazing forage mass and the post-grazing forage mass of the previous cycle. The accumulation rate (kg DM ha-1 day) was calculated by dividing the accumulation by the grazing interval. The net accumulation rate (kg MS ha-1 day) was obtained by subtracting the accumulation rate of dead tissue from the sum of the rates of accumulation of leaf blades. The accumulation of forage mass of piatã grass increased linearly with nitrogen fertilization and is influenced by the time of the year, presenting smaller yields in the winter. The 18 increase of the forage production through nitrogen fertilization reflected in the increase of the animal stocking rate when used under intermittent grazing with variable stocking rate. Experiment 3: The samples were cut at the soil level to the pre and post-grazing condition. These samples were then taken to the bromatology laboratory and manually fractionated in leaf blades, pseudocolmo (stem + leaf sheaths) and dead tissue (dead + senescent) to determine the percentage of morphological components of the forage mass. The agronomic efficiency of the applied nitrogen was determined according to the following formula: Forage mass with fertilization (kg) - forage mass without fertilization (kg) / Dose of N (kg); in kg of DM / kg N. The application of nitrogen increased the dry matter yield of leaves and stalks, provided an increase in the leaf: stem ratio with an increase in the number of cycles and a reduction in the grazing interval period. The highest efficiency of nitrogen utilization was obtained with a dose of 450 kg of N / ha / year with a minor difference of the lowest dose (150 kg of N / ha / year). Experiment 4: In order to determine the nutritive value of the pastures, the plant material was collected inside four metal frames of 0.25 m2 above the intended 20 cm residue in the pre-grazing condition during the entire experimental period. Simple samples were taken from the four frames which then became a composite sample. An aliquot of this sample was submitted to pre-drying, and an aliquot was removed, which were pre-dried in a forced ventilation oven at 60ºC, for approximately 72 hours, and then milled in a Willey type mill using sieves with 1mm sieves for analysis of dry matter, organic matter, crude protein, mineral matter, neutral detergent fiber and hemicellulose. Nitrogen fertilization with the dose of 450 kg of N/ha/year and the seasons of the final year of summer / autumn, spring and summer contributed to the better chemical composition of piatã grass. Experiment 5: imaging was performed by means of a remotely piloted fixed-wing aircraft with a 16-megapixel camera. The orthortified mosaic was generated in the agisoft photoscan software from the photographs with central coordinates, obtained was of 5 cm. The vegetation indices were generated in the raster calculator of the QGis 2.14 software. It can be observed from a visual interpretation of the ortoretificado mosaic that the treatments with doses above 300 kg ha-1 of nitrogen had vegetation with intense green color, demonstrating greater vigor in these pastures. Vegetation indexes showed good results in pasture monitoring and can be used as tools to assist in the proper management of nitrogen fertilization in pasture areas, as well as the evaluation of areas with soil exposed to the resection of the species from the coverage mapping from soil. The SPAD index represents a positive evaluation of the chlorophyll index in the leaves of the piatã grass.