Effects of Soil Fertility Management on the Diversity of Rhizobacteria in Millet Fields in Niger

Agriculture in sub-Saharan Africa, and particularly in Niger, is constrained by low productivity, recurrent drought, limited access to fertilisers and environmental degradation, all of which contribute to persistent food insecurity. Rhizobacteria are recognised as important components of the rhizosphere because they can support plant growth and may reduce dependence on chemical fertilisers. However, the response of rhizobacterial communities to farmers’ soil fertility management practices in millet fields remains insufficiently documented. This study analysed the effect of farmers’ soil fertility management practices on rhizosphere microorganisms. The research was conducted from 2015 to 2017 in three villages (Lélédjé, Moli Haoussa and Alambaré) located near Niger’s W National Park. Experimental plots of 16 m² were arranged in scattered blocks and subjected to animal penning, mulching, manure application and control treatments. The plant material was a local millet variety, somno (Pennisetum glaucum (L.) R. Br.). A total of 36 composite soil samples were analysed over the three years. Bacteria were isolated on five culture media, and colony numbers were expressed as colony-forming units per gram of soil. The highest bacterial counts were recorded on PCA and King A and B media, followed by PCA + GNO, whereas lower counts were observed on EMB and GNO media. Bacterial colony density differed among treatments, with animal penning and manure application producing higher densities than mulching and the control. These findings indicate that traditional soil fertility management practices used by farmers can maintain soils that are densely populated with cultivable rhizobacteria. Such practices may contribute to locally accessible strategies for improving soil biological fertility in millet-based farming systems in Niger.