Field evaluation of N2-fixation and N-utilization by phaseolus bean varieties determined by15N isotope dilution* |
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Authors: | Alaides P Ruschel P B Vose E Matsui R L Victoria S M Tsai Saito |
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Institution: | 1. Centro de Energia Nuclear na Agricultura (CEN A), Caixa Postal 96, 13400, Piracicaba, S?o Paulo, Brasil
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Abstract: | Summary Differences in N2-fixation byPhaseolus vulgaris bean cultivars were successfully evaluated in the field using15N isotope dilution technique with a non-fixing test crop of a different species (wheat). The Phaseolus cultivars could have
been similarly ranked for N2-fixation capacity from either seed yield or total nitrogen yield, but the isotope method provided a direct measure of N2-fixation and made it possible to estimate the proportion of fixed to total nitrogen in the crop and in plant parts.
Amounts of nitrogen fixed varied between 24.59 kg N/ha for the 60-day cultivar Goiano precoce to 64.91 kg N/ha for the 90-day
cultivar Carioca. The per cent of plant nitrogen due to fixation was 57–68% for the 90-day cultivars and 37% for Goiano precoce
(60-day cultivar).
Fertilizer utilization was 17–30% of a 20 kg N/ha fertilizer application. 100 kg N/ha fertilizer application decreased N2-fixation without suppressing it totally.
Differences in yield between the highest yielding (Carioca) and the lowest (Moruna) 90-day cultivars were also due apparently
to varietal differences in efficiency of conversion of nitrogen to economic matteri.e. seed, as well as to differences in capacity of genotypes for N2-fixation.
The work described here was in part supported by IAEA Research Contract No. RC/2084
UNDP/IAEA Project BRA/78/006 |
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Keywords: | Isotope techniques Nitrogen-15 Nitrogen fixation Nitrogen utilization Phaseolus vulgaris Rhizobium Varietal comparison |
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