Effects of Bradyrhizobia inoculation on specific and promiscuous Soybean and common bean varieties in poor sandy soils in Zimbabwe

Abstract Rhizobial inoculation is pivotal in improving legume crop yields for most smallholder farmers as native soils are often low in rhizobial populations. A study was conducted in Zimbabwe to determine the response of selected common bean and soybean varieties to inoculation without the limitation of P, K, S, Ca and Mg. Both specific and promiscuous varieties of soybean were used. Grain yield for all the specific soybean varieties (SC Squire, SC Saga and PAN 147) responded positively to inoculation and grain yields increased by about 100 %. Un-inoculated specific soybean varieties yields ranged from 150 kg ha-1 in SC Squire to 250 kg ha-1 in SC Saga. Biomass and grain yields of promiscuous varieties showed no response to inoculation. In common bean, response to inoculation varied with variety but generally no significant differences were recorded. Speckled ice, Bounty and Cardinal recorded higher but non-significant grain yield in inoculated fields compared to un-inoculated crops. Biomass yields in Speckled ice, Bounty, Cardinal and PAN 148 were higher in inoculated treatments (though not significant) compared to un-inoculated. We conclude that in poor sandy soils it remains necessary to inoculate specific soybean varieties as yields double when inoculants are used, while there seems to be no benefit in using inoculants for common bean and promiscuous soybean varieties. Key Words: soybean, commonbean, rhizobial inoculation,