02777naa a2200301 a 450000100080000000500110000800800410001910000160006024500750007626000090015152019180016065000120207865000190209065000230210965000250213265300330215765300080219065300190219865300080221765300400222570000280226570000190229370000230231270000200233570000170235570000180237277300850239015984782001-02-26       2001    bl ---       0--  u    #d1 aREIS, V. M.  aBiological nitrogen fixation associated with tropical pasture grasses.  c2001  aThe semi-humid or humid tropics are ideal for the production of large quantities of biomass from fast-growing C4 grasses, but high yields normally require large quantities of fertiliser, especially N, which has a very high input from fossil fuels (natural gas). A program has been started recently to use elephant grass (Pennísetum purpureum Schum.) to substitutefirewood as a fuel and also to make charcoal for iron production. In this case, any large N fertiliser additions would mean that the yield of bio fuel per unit of fossil fuel invested would bc detrimentally affected. In this study, we report on the potential for the selection of genotypes of fast-growing C4 tropical grasses of the genera Pennisetum and Brachiaria for their capacity to obtain N inputs from plant-associated biological nitrogen fixation (BNF). Fourteen genotypes each of Brachiaria and Pennisetum were screened for BNF contributions by growing them in 15N-labelled soil. In the case of the Pennisetum, after a suitable cuning height for the crop had been selected, there were large differences in dry matter production, N accumulation and 15N enrichment. The differences in 15N enrichment between genotypes were statistically significant and BNF inputs were estimated as high as 41% of accumulated N. In the study on Brachiaria genotypes, potential inputs of BNF seemed lower. Only one or two genotypes of B. brizantha and B. ruziziensis obtained more then 20% of their N from BNF. The N2-fixing bacteria that were most commonly associated with shoots and roots the Pennísetum genotypes were of the genus Herbaspirillum, but predominantly of a recently described new species. The Brachíaria spp. from three different sites! Rio de Janeiro, Goânia, Bahia) were predominately colonised by Azospirillum spp., most of the isolates being of the species Azospirillum amazonense. Very few Herbaspirilla were isolated from these plants.  agrasses  aCapim Elefante  aGramínea Tropical  aPennisetum Purpureum  aBiological nitrogen fixation  aBNF  aElephant grass  aFBN  aFixação biológica de nitrogênio1 aREIS JÚNIOR, F. B. dos1 aQUESADA, D. M.1 aOLIVEIRA, O. C. de1 aALVES, B. J. R.1 aURQUIAGA, S.1 aBODDEY, R. M.  tAustralian Journal of Plant Physiology, Victoriagv. 28, n. 9, p. 837-844, 2001.