Symbiotic N sub(2) fixation in 30 field-grown cowpea (Vigna unguiculata L. Walp.) genotypes in the Upper West Region of Ghana measured using super(15)N natural abundance

• Published in: Biology and fertility of soils Vol. 46; no. 2; pp. 191 - 198
• Main Authors: Belane, Alphonsus K, Dakora, Felix D
• Format: Journal Article
• Language: English
• Published: 01.02.2010
• Subjects: Vigna unguiculata
• ISSN: 0178-2762; 1432-0789
• DOI: 10.1007/s00374-009-0415-6

In this study, 30 cowpea genotypes were assessed for symbiotic N sub(2) fixation in 2005, and 15 of them were re-evaluated in 2006 using the super(15)N natural abundance technique. Shoot dry matter yield of cowpea genotypes increased significantly in cvs. Vuli-1, Glenda, IT93K-2045-29, IT90K-59, Omondaw, Apagbaala, and IT84S-2246 in 2005 producing about 3.0 to 3.6-fold more biomass relative to cv. Vallenga. In 2006, seven out of the 15 cowpea genotypes tested (namely, IT97K-499-39, TVu11424, Botswana White, IT84S-2246, Sanzie, Brown Eye, and Glenda) also produced more dry matter than cv. CH14. Shoot d super(15)N values ranged from -0.58ppt to 1.49ppt in 2005, and -1.51ppt to 1.40ppt in 2006, and these resulted in %Ndfa values of 63.5-86.7% and 56.2-96.3%, respectively. The amount of N-fixed was 49-178kgN ha super(-1) in 2005 and 62-198kgN ha super(-1) in 2006. Furthermore, there was a direct relationship between the level of symbiotic N nutrition and plant growth, and between grain yield and amount of N-fixed in 2005 and 2006. As a result, genotypes that fixed the most N also produced the largest biomass and the greatest amount of grain yield. The observed relationship between N sub(2) fixation and biomass confirmed our view that cowpea (and other grain legumes) can be concurrently selected for higher N sub(2) fixation, superior plant growth, and greater grain yield. The high levels of N-fixed by many of the cowpea genotypes in this study suggest that they can contribute large amounts of N to cropping systems in African agriculture.