Symbiotic N fixation in 30 field-grown cowpea (Vigna unguiculata L. Walp.) genotypes in the Upper West Region of Ghana measured using p#eN natural abundance

摘要

In this study, 30 cowpea genotypes were assessed for symbiotic N fixation in 2005, and 15 of them were re-evaluated in 2006 using the p#eN 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 tp#eN values ranged from 0.58 to 1.49 in 2005, and 1.51 to 1.40 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 49-178 kg N hap# in 2005 and 62-198 kg N hap# 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 fixation and biomass confirmed our view that cowpea (and other grain legumes) can be concurrently selected for higher N 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.