Exploring the benefits of inoculated cowpeas under different climatic conditions in Namibia

Abstract

Cowpeas (Vigna uniculata L. Walp) are grown by many smallholder farmers in sub-Saharan Africa for food and their ability to fix nitrogen even under stress. Their performance depends on the indigenous rhizobial strains that live in symbiotic association with the roots; it can be enhanced if the seeds are inoculated with more effective ones. Data of the effectiveness of the technique under a variety of climatic conditions is rare. Here, we thus use a model to upscale two field experiments conducted in Namibia to include different climate change scenarios. The simulations show that non-inoculated cowpeas have mean yields of 0.5 t/ha and inoculated cowpeas 1 t/ha. If climatic conditions are favorable (cool and wet), estimated yield differences increase to over 1 t/ha. In dry years (< 200 mm), the average yield difference is only 0.1 t/ha. In the far future (2080–2100), instances of dry and hot years will increase. Using inoculated cowpea seeds instead of non-inoculated ones thus does not benefit farmers as much then as in the near future (2030–2050). In conclusion, using cowpea seeds inoculated with an efficient rhizobial strain can significantly increase yields under varying climatic conditions, but yield advantages decrease markedly in very dry and hot years.

"Effects of a New Rhizobium-Based Biofertilizer (Fertiriz) on Growth and the Yield of Cowpea (Vigna unguiculata (L.) Walp)"

“…Different researchers reported that rhizobia inoculation increased the yield in some studies on different species [23,26]. In an experiment conducted in Namibia under different climatic conditions in cowpea yields improved on average by 47% [46]. In the same way, in our study, cowpea var 'Cubanita 666' yields increased around 62% when Rhizobium (Fertiriz) was combined with 50% of mineral fertilizer NPK (in chambers assay), and 47% using only the biofertilizer (in the field), compared with the non-inoculated treatment.…”