02417naa a2200361 a 450000100080000000500110000800800410001910000180006024501080007826000090018652014390019565000170163465000120165165000190166365000130168265000110169565000140170665000160172065300310173665300310176765300080179865300210180665300120182765300080183965300120184765300390185965300130189865300290191165300200194065300150196070000190197577300610199416208801996-09-17       1995    bl ---       0--  u    #d1 aBODDEY, R. M.  aNitrogen fixation associated with grasses and cerealsbRecent progress and perspectives for the future.  c1995  aOver the last 20 years many new species of N2-fixing bacteria have been discovered in association with grasses, cereals and other non-nodulating crops. Virtually all of these bacteria are microaerophylic, fixing N2 only in the presence of low partial pressures of oxygen. Until a few years ago much attention was focussed on members the genus Azospirillum and it was assumed that N2 fixation was restricted to the rhizosphere or rhizoplane of the host plants. Through the use of N balance and 15N techniques it has been shown that in the case of lowland rice, several tropical pasture grasses and especially sugar cane, the contributions of biological N2 fixation (BNF) are of agronomic significance. More detailed study of the N2-fixing bacteria associated with sugar  cane (Acetobacter diazotrophicus and Herbaspirillum spp.) has shown that they occur in high numbers not only in roots of this crop but also in the stems, leaves and trash but are rarely found in the soil. Some of these endophytic diazotrophs have now also been found in forage grasses, cereals, sweet potato and cassava, although evidence of significant BNF contributions is still lacking. The identification of these endophytic diazotrophs as the organisms probably responsible for the high contributions of N2 fixation observed in sugar cane suggests that it may be possible to attain significant BNF contributions in some other gramineae and perhaps root crops.  aAzospirillum  agrasses  aHerbaspirillum  anitrogen  aCereal  aGramínea  aNitrogênio  aAcetabacter diazotrophicus  aAcetobacter diazotrophicus  aBNF  aCana-de-açúcar  aCereals  aFBN  aFixacao  aFixação biologica de nitrogênio  aFixation  aNitrogen fixing bacteria  aPlanta graminea  aSugar cane1 aDOBEREINER, J.  tFertilizer Research, Dordrechtgv. 42, p. 241-250, 1995.