Nodulation, Nitrogen Yield and Fixation by Bambara Groundnut (Vigna Subterranea (L.)Verdc.) Landraces Intercropped with Cowpea and Maize in Southern Guinea Savanna of Nigeria

Two separate field experiments were undertaken during the rainy seasons (August – December) of 2010 and 2011 at the Teaching and Research Farm of the Federal University of Agriculture, Makurdi, Nigeria. The objective of the study was to evaluate some landraces of bambara groundnut intercropped separately with cowpea and maize at varying planting densities for nodulation, nitrogen (N) yield and fixation. Each experiment was a 2 x 3 x 3 split-split plot set out in a randomized complete block design with three replications. Intercropping decreased the number and weight of nodules; nitrogen derived from the atmosphere and fixed in both bambara groundnut/maize and bambara groundnut/cowpea intercropping systems. No significant differences were noticed between the landraces in N content of shoot and roots, but ‘Okirikiri’ had significantly higher N content (3.11 %) of pod with seed than the other two landraces. ‘Okirikiri’ and ‘Adikpo’ landraces fixed more N than ‘Karo’. N fixed increased with decline in bambara groundnut planting density. Mean percentage of plant N derived from atmosphere varied from 49.80 in the bambara groundnut/maize systems to 56.80 in the bambara groundnut/cowpea intercrops, while N fixed was 11.27 kg/ha and 34.90 kg/ha in the respective intercrop systems. The expectation of enormous contribution of nitrogen fixation to bambrara groundnut yields and its residual effects on soil medium for ensuing crops may be an illusion with the use of the landraces tested in this work, except, probably when inoculated with the appropriate rhizobia?