Selection of sugar cane cultivars for associated biological nitrogen fixation using 15N-labelled soil

The contribution of associative and symbiotic nitrogen fixation to the nitrogen nutrition of non-legumes

“…The difficulty has been in obtaining a non-fixing reference plant. The approach adopted by Boddey and co-workers for C4 grasses (Boddey and Victoria, 1986;Boddey et al, 1983;Lima et al, 1987;Miranda and Boddey, 1987;Miranda et al, 1990;Urquiaga et al, 1989) can be recommended, where cultivars exhibiting little or no associative N 2 fixation were identified and used as reference plants.…”

“…Experiments with sugar cane have been carried out in Brazil in large pots containing 60-120 kg soil (de Freitas et al, 1984;Lima et al, 1987) or a concrete tank containing 80 t soil (Urquiaga et al, 1989) located in the field (Table 3). Biologically-active, uninoculated soils were used.…”

“…While recognising the error involved in extrapolating fixation in pots to the field situation, Lima et al (1987) calculated that associative N 2 fixation could potentially contribute 2 0 0 k g N h a -~ to the N nutrition of CB 4789. Work with seven commercial cultivars grown in the field for 250 days (Urquiaga et al, 1989), including several cultivars used by de Freitas et al (1984) and Lima et al (1987), indicated that all had a greater N yield and a lower 15N enrichment compared to Brachiaria radicans, the nonfixing reference plant. The percentage of plant N estimated to be derived from N 2 fixation ranged from 42-52% (84-128 kg N ha-l).…”

“…Although 100-200 kg N ha 1 is removed in every cane harvest, the N fertility of soils is generally maintained despite continuous cropping with low fertilizer N inputs (Lima et al, 1987). While no microbiological investigations were carried out in conjunction with the isotope dilution studies, Urquiaga et al (1989) suggested that the novel N 2 fixing bacterium, Acetobacter diazotrophicus, isolated from the stems and roots of sugar cane at various sites in Brazil (Cavalcante and D6bereiner, 1988), would be a strong candidate.…”

Assessment of nitrogen fixation inPterocarpus erinaceusandP. lucensusing15N labeling techniques

“…Nitrogen (N%) and atom % 15 N excess were determined at the CNPBS-EMBRAPA laboratory in Rio de Janeiro, Brazil. Total N was determined using an automated nitrogen analyzer according to Bremner (1965); N isotope ratio analysis was performed on a VG Isogas 900 mass spectrometer (VG Isogas, Middlewich, UK) according to Urquiaga et al (1989). N 2 fixation was assessed by both the A value method (Fried & Broeschart, 1975) and the direct isotope dilution (Fried & Middleboe, 1977) equations.…”