Potencial produtivo e eficiência da fixação biológica de nitrogênio de cinco genótipos de capim elefante (Pennisetum purpureum Schum.), para uso como fonte alternativa de energia

Abstract

Elephant grass (Pennisetum purpureum Schum.) is one of the grasses known for its great capacity for dry matter accumulation, having also other characteristics favorable for the energy production. The objective of this study was to select elephant grass genotypes for high biomass yield, nitrogen accumulation and contribution of Biological Nitrogen Fixation (BNF), and to analyze the influence of cultivation on soil carbon and nitrogen stocks of different soils. Two studies were conducted at two sites located in Anchieta, Espírito Santo State, and Seropédica, Rio de Janeiro State, with different climate and soil conditions. The experimental design used in both experiments was factorial in randomized complete blocks, with four replicates. The genotypes used in Anchieta study site were: Cameroon, BAG, CNPGL F 06-3, CNPGL F 79-2, and Gramafante. In the experiment conducted in Seropédica, there were used the same genotypes with the replacement of genotype CNPGL F 79-2 by genotype Roxo. The dry matter production of the different genotypes ranged from 39 to 47 Mg MS ha- 1 when the genotypes were grown in Anchieta, after 18 months of cultivation. The values were between 44 and 66 Mg MS ha- 1 when grown in Seropédica, in 21 months of cultivation, over three harvests. The total nitrogen accumulated in the aerial biomass ranged from 221 to 342 kg ha-1, when the genotypes were grown in Anchieta, and between 250 to 332 kg ha-1, when grown in Seropédica. The genotype that showed the greatest N accumulation and biomass yield were: Cameroon, CNPGL F 06-3 and CNPGL F 79-2, followed by BAG. The results of the estimates of BNF contribution were very promising for all genotypes, at both study sites, and values of up to 54 % for CNPGL F 06-3 were observed. With regard to the C/N ratio, levels of fiber, cellulose, lignin, which describe biomass quality, in general, were not influenced by the difference in the fertility of the different soils. These results demonstrate the potential of elephant grass for energy production. The contents of ash were within the normal levels for the plants, below 5%, calling attention only for the leaf values, which were significantly lower. Thus, the elephant grass showed qualitative and quantitative favorable characteristics to be used as source of renewable energy, and the Cameron, BAG, CNPGL F 06-3, and CNPGL F 79-2 genotypes were the best fitted for charcoal production for usage in the steel industry.