Endophytic Diazotrophs in Sugar Cane, Cereals and Tuber Plants

Abstract

Plant breeding with low N fertilizer levels has now been shown to be the key to the high contributions of biological dinitrogen fixation (BNF) to graminaceous plants. Due to historically high prices of N fertilizers in Brazil, cereals, forage grasses and especially sugar cane have been bred, or selected, for decades with very low N fertilizer levels, and with this involuntarily, for BNF. During the last two decades nitrogen balance experiments with rice (App et al., 1980; App et al., 1984; Ito et al., 1980), 15N2 incorporation (De-Polli et al., 1977) and 15N dilution experiments with forage grasses (Boddey, Victoria 1986; Miranda, Boddey 1987) and rice (Urquiaga et al., 1991) clearly showed that in certain genotypes substantial contributions of BNF can be obtained. Recent experiments using N balance (Lima et al., 1987) and the 15N dilution method with various sugar cane genotypes, showed that this crop can obtain more than 60% of its nitrogen needs from BNF under field conditions (Urquiaga et al., 1992). Most sugar cane cultivars in this experiment grown in an extremely N deficient subsoil (0.08% total N) irrigated and fertilized with PK and minor elements alone, produced yields more then twice the Brazilian average (60 t.ha-1) in three consecutive harvests. The two most outstanding cultivars CB45-3 and SP 70–1143 produced 244 and 182 t.ha-1, yr-1 respectively obtaining 154 and 134 kg N.ha-1.yr-1 from BNF (means of three harvests).