Fate of Rhizosphere Microorganisms and Growth of Leguminous Plants in Cassava Mill Effluent Simulated Soil

Aims: The aim of this study was to determine the effect of cassava mill effluent in simulated soil on rhizosphere microorganisms and growth of leguminous plants. Methodology and Results: The fate of rhizosphere microbes and growth of leguminous plants in cassava mill effluent simulated soil was evaluated using standard physical, microbiological and biochemical techniques. The results showed that the number of buds, leaves and nodules formed fluctuated across the concentration. The fungal isolates from the cassava mill effluent simulated soil were virtually the same across the concentration gradients of 0%, 10%, 20%, 30%, 40%, 50% and 100%, the only difference was that different fungal genera were found in plots where different leguminous plants were used for the simulation experiment. C. mucunoides at cassava mill effluent (CME) impacted plots (0%-100%) had Saccharomyces sp. and Mucor indicus as it’s predominant fungal isolate while the C. pubescens from the same site had Fusarium sp. and Gliocladium sp. as its predominant fungal isolates. Cassava mill effluent (CME)-simulated soil (0%-100%) had Chromobacterium sp. and Corynebacterium sp as it’s predominant bacterial isolates from the Centrosema pubescens plots. Calopogonium mucunoides plots had Bacillus sp., Acinetobacter sp. and Escherichia coli as it bacterial isolates. Same nitrogen-fixing bacteria were isolated from all the cassava mill effluent simulated plots (0%-100%) irrespective of the legume planted for the phytoremediation exercise. The nitrogen-fixers isolated were: Azotobacter sp., Azospirillum sp., Frankia sp., Bradyrhizobium sp., Hebaspirillum sp., Cyanobacteria (or blue green algae) and Anabaena sp. Other isolates were Nostoc sp., Clostridium sp. and Rhizobium sp. Conclusion, Significance and Impact of Study: The simulation experiment analysis revealed that soil acidity influences many chemical and biological characteristics of soil including availability of nutrient and toxicity of metals which can also affect microbial community in many ways. It also revealed that acidic soils can significantly reduce nodulation and nodule function in leguminous plants.