Encontro de Energia no Meio Rural
AGRENER

Abstract

QUESADA, Diego Mureb, FRADE, Cátia, RESENDE, Alexander et al. A fixação biológica de nitrogênio como suporte para a produção de energia renovável.. In: ENCONTRO DE ENERGIA NO MEIO RURAL, 3., 2000, Campinas. Proceedings online... Available from: <http://www.proceedings.scielo.br/scielo.php?script=sci_arttext&pid=MSC0000000022000000100031&lng=en&nrm=abn>. Acess on: 31 Oct. 2024.

Recently, rapid-growing grasses which possess the C4 photosynthetic pathway such as Miscanthus and Pennisetum spp. have been considered as prime candidates for the production of bio-fuels. In the case of Pennisetum purpureum (Elephant grass) and related hybrids, the genotypes studied until now have generally been selected for high production of forage for cattle under high N fertiliser additions. For forage production it is desirable that the tissues have high protein content. However, for biomass production the priority should be for carbon accumulation and the highest possible biomass production per unit of applied fertiliser. The manufacture of N fertiliser involves a very high cost in terms of fossil energy, and if large additions are made the grass biomass produced may have only a little more (or even less) calorific value than that utilised in the manufacture of the fertiliser. This completely negates the prime objective of biofuel production which the replacement of energy derived from non-renewable fossil sources with that derived from solar radiation. Recently the team headed by Dr Johanna Döbereiner at Embrapa Agrobiologia have shown that several tropical grasses (including sugar cane and elephant grass) are able to obtain significant quantities of N through the action of associated endophytic N₂-fixing bacteria. Derived from this line of reasoning a study is being conducted in the field to select appropriate genotypes of Pennisetum purpureum which are efficient is biomass production in soil of very low N fertility. In the first stage four genotypes have been selected : Gramafante, Cameroon, BAG 02 and Roxo, which have been the most productive over a 5 year period without N fertiliser addition. A complementary study is underway to evaluate biomass production and quantify the N₂ fixation input. Preliminary results are promising and show that these materials produce well without N fertiliser application a with a contribution of approximately 30 % of plant N derived from N₂-fixing, which can be regarded as very satisfactory for a graminaceous specie.

Keywords : Biomassa; Bactéria Diazotrófica; Energia; Fixação Biológica de Nitrogênio; Pennisetum purpureum.