Nodulation, Biomass Production and Yield of Some Indigenous Legumes as Influenced by Rhizobium Inoculation in the Rainforest Agro-ecological Zone of Nigeria

Aim: A field study was conducted during the late cropping seasons of 2015 and 2016 at Akamkpa (latitude 5°15’ N and longitude 8°22’ E), south southern Nigeria, to evaluate the response of some legume genotypes to seed inoculation with NoduMax, a Rhizobium inoculant developed by the International Institute of Tropical Agriculture (IITA).

Study Design and Methodology: Treatments were factorial combinations of inoculated and non-inoculated seeds of Cowpea, Groundnut, Bambara groundnut, Bebi (Viny Lima) bean, Mucuna bean, and African yam bean, laid out in randomized complete block design replicated thrice.

Results: The response of the test crops to inoculation varied with growth stage. At the seedling stage, effective nodule number was not significantly affected in all but Mucuna bean in which there was a 42.7% reduction. At pre-anthesis, Bambara groundnut, Bebi bean, Groundnut, and Cowpea recorded a statistically similar number of nodules (p=0.05) under inoculated and non-inoculated conditions, but inoculation reduced nodule formation in Mucuna bean and African yam bean by 22.4 and 20.4%, respectively. Nodule dry weight of Bebi bean, Bambara groundnut, Mucuna bean and Cowpea was unaffected by inoculation when assessed at the seedling and pre-anthesis growth stages, but that of Groundnut was reduced by 35, and African yam bean increased by 60%, respectively. Inoculation increased the nodule dry weight of African yam bean and Mucuna bean by 56.5 and 60.6% at seed initiation stage, and reduced that of Bambara groundnut and Groundnut by 25.6 and 50.0%, respectively. The effect of genotype × inoculation interaction on plant biomass and fresh grain yield was significant; whereas inoculation significantly increased the yield of Cowpea from 2,471 to 2,794 kg/ha and 2,995 to 3504 kg/ha in 2015 and 2016, respectively, it did not significantly affect that of Bebi bean, African yam bean and Bambara groundnut. On the contrary, the yield of groundnut was reduced from 884 to 560 kg/ha and 963 to 678 kg/ha in 2015 and 2016, respectively.

Conclusion: Inoculation with NoduMax was beneficial to cowpea, but did not significantly improve the performance of Bebi bean, and Groundnut. It could be that Bebi bean is promiscuous and better adapted to the native strains of Rhizobium, while the Rhizobium in Groundnut is antagonistic and incompatible with the introduced inoculants.