Abstract

The objective of this study was to investigate varietal differences in symbiotic nitrogen fixation (SNF) and redistribution of N in the leaves and stems. Five Andean genotypes Sisi, Bukoba, Red Hawk, Mecost and Cardinal were evaluated for SNF and N redistribution in a field trial conducted at University of Zambia, Lusaka, Zambia. Nitrogen derived from the atmosphere (NDFA) ranged from 15.9 kg ha-1 (Cardinal) to 48.4 kg ha-1 (Mecosta) with an average of 30.9 kg ha-1. Significant differences in N redistributions in the leaves and stem were observed. Both Mecosta and Red Hawk, which comparatively had higher NDFA, also had high redistribution of N from the leaves for Red Hawk and from the stem for Mecosta. This result suggest that despite Mecosta and Red Hawk being superior in SNF, both had significant dependency on the N redistributed mainly from the leaf and stem, respectively, to meet their seed N requirements and support high seed yield. This result confirms the important role of N redistribution in common bean from stems and leaves regardless of the SNF ability of a genotype. Mecosta, which had the highest NDFA, also had highest seed yield (1925 kg ha-1), providing further evidence on the important role of SNF in common bean productivity especially in Africa where farmers do not apply N fertilizers to common bean.

Keywords: Nitrogen, symbiotic nitrogen fixation, nitrogen derived from atmosphere, nitrogen redistribution.