Soybean Varieties, Developed in Lowland West Africa, Retain Their Promiscuity and Dual-Purpose Nature Under Highland Conditions in Western Kenya

Abstract

Entry points that give farmers immediate benefits are required to reverse the ever-declining soil fertility status of a substantial area in sub-Saharan Africa. In West Africa, dual-purpose, promiscuous soybeans (Glycine max (L.) Merr.) that produce a substantial amount of grains and leafy biomass and do not require inoculation with specific Rhizobium spp. strains were developed and have increased resilience of farming while providing income to farmers. These crops could be a potential entry point for soil fertility improvement in western Kenya, provided they retain their promiscuity and dual-purpose character in this new environment. The major objective of this work was to quantify nodulation, biomass production and grain yield characteristics of a set of best-bet, dual-purpose varieties relative to a locally available variety at two sites (Vihiga and Siaya districts) in western Kenya. In the presence of P, most promiscuous soybean varieties showed substantial improvements in nodulation (19–165 nodules per 0.5 m of soybean) than did the local variety (3–13 nodules per 0.5 m of soybean). While grain yield was for all but one variety as good as the local control (845 kg ha^–1, on average), nearly half of the varieties produced significantly higher amounts of biomass at 50% podding than did the local variety (865 kg ha^–1 in Siaya and 1877 kg ha^–1 in Vihiga). Increases in nodulation, biomass production and grain yield were mainly observed after application of P fertilizer; in the absence of P, almost none of the varieties performed better than the local control for any of the measured characteristics. To fully exploit the potential soil fertility-improving characteristics of these varieties, it will be necessary to facilitate availability of P fertilizer and to foster demand for soybean at the farm, community and national levels.