Produ??o de capim elefante (Pennisetum purpureum Schum.) para fins energ?ticos no Cerrado: Resposta ? aduba??o nitrogenada e idade de corte

• Autor(a) principal: Flores, Rilner Alves
• Data de Publicação: 2009
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFRRJ
• Texto Completo: https://tede.ufrrj.br/jspui/handle/tede/294
• topic: biomassa; 15N; bioenergia; biomass; 15N; bioenergy; Agronomia

The elephant grass species (Pennisetum purpureum Schum.) is among the grasses of greater capacity for dry matter accumulation, but it also has favorable quality characteristics for use in energy production, such as high fiber content, high C/N ratio, high calorific value and low ash content. However, the objective of this study was to assess elephant grass genotypes efficient for biological nitrogen fixation (BNF), and to conform the harvesting time and nitrogen fertilization management for high production of biomass for usage as an energy source in the soil and environmental conditions of the Cerrado. Two field studies were conducted in areas of Oxisols, located in the municipality of Gurupi, Tocantins State, Brazil. Both experiments were set as randomized block split plot with four replications. The first study evaluated two genotypes of elephant grass: Purple and Paradise, fertilized or not with nitrogen. It was conducted only one cut of elephant grass, 180 days after planting, in order to evaluate the biomass production, efficiency of BNF, and the quality of the material produced. In the second study it was evaluated the effect of nitrogen fertilization in determining the best time to harvest the grass for high production, efficiency of BNF, and quality of biomass. The grass genotype used was the Paradise. In the first experiment, the production of dry matter (DM) of the two genotypes ranged between 30 and 42 Mg DM ha-1. In the second one, a quadratic adjustment for levels of nitrogen fertilization for production of DM was performed, where highest production was obtained with 50 kg N ha-1, resulting in 32 Mg DM ha-1, and the best harvesting time for biomass production was at 180 days after planting, producing an average of 34 Mg DM ha-1. In relation to the total N accumulated, values ranged between 347 and 539 kg ha-1 in the first experiment, where the genotype Purple accumulated more shoot nitrogen in relation to genotype Paradise. In the second experiment evaluating the effect of nitrogen fertilization, the N accumulation ranged between 323 and 403 kg ha-1, and the dosage of 50 kg ha-1 N promoted most N accumulation by the plant. The greatest accumulation of N was observed in the largest harvest interval (180 days after planting), of about 422 kg N ha-1. Regarding the BNF efficiency in the study conditions of both experiments, the contribution was less than 10%, consistent with the high soil fertility of the area in study. The C/N ratio, leaf / stem ratio (C/F), soluble fiber, phosphorus and potassium levels, and calorific value presented by the elephant grass with regard to the quality of material produced, in general, were not affected by difference of the management conditions of the elephant grass. On average, the C/N ratio was of 40, the C/F was around 5, and the calorific value was of about 4.000 kcal / kg, in both experiments. In relation to the levels of fiber produced, the genotype Paradise was higher than the Purple, producing over 60%, while the Purple produced about 50%. The contents of ash produced were close to those usually found in grass plants, about 5% on average. Thus, the elephant grass presented qualitative and quantitative characteristics that were positive for its usage in renewable energy production in the Cerrado region, and the genotypes Purple and Paradise were highly promising for this. .