Soybean (Glycine max) and maize (Zea mays) production as influenced by rhizobia inoculation and cropping systems in western Kenya

The use of promiscuous varieties and commercial inoculants has been shown to increase soybean production and improve soil fertility. However, most cropping systems are characterized by indigenous bradyrhizobia whose populations are often low or ineffective and can be increased in the presence of the host legume for several seasons. The contribution of a commercial inoculant in soils with low levels of indigenous rhizobia to soybean and maize production in different cropping systems was evaluated in field experiments in three sites in Siaya County in Kenya using a completely randomized block design. Maize and soybean were planted as sole crops or in rotations for four seasons (short rain (SR) 2014, long rain (LR) 2015, SR 2015 and LR 2016). Soybean grain yields increased significantly under rotation when maize and soybean were planted in the LR and SR, respectively. A strong, significant and positive correlation between soybean grain yield and nodule weight was recorded. The inoculated and non-inoculated soybean-maize system recorded a rotational yield gain of 15.7% and 7.3% in LR 2015, 24.9% and 24% in LR 2016, respectively. These findings give a scientific validation of the yield responses and seasonal implications of the choice of crop that the farmer makes in a rotation. Further research on economic profitability and isolation of the native strains and bacterial diversity in the study soils is needed so as to validate the results on nodulation and yields.