Effect of Fertilization on the Dynamics and Activity of Iron-Reducing Bacterial Populations in a West African Rice Paddy Soil Planted with Two Rice Varieties: Case Study of Kou Valley in Burkina Faso

Abstract

Iron toxicity is a major stress to rice caused by a high concentration of reduced iron, in the soil in many lowlands worldwide. To reduce iron toxicity in the West African lowlands, an investigation was performed at the site of the University of Ouagadougou, in pots containing an iron toxic soil from the Kou Valley (West of Burkina Faso). The experiment objective was to study the effect of mineral fertilizer on Iron Reducing Bacteria (IRB) dynamics and activity during rice cultivation, iron accumulation in rice plant and rice biomass yield under iron toxicity conditions. BOUAKE-189 and ROK-5 rice varieties, sensitive and tolerant to iron toxicity, respectively, were used for the experiment. The pots were amended with chemical fertilizers (NPK + Urea and NPK + Urea + Ca + Mg + Zn complex). Control pots without fertilization were prepared similarly. The kinetics of IRB and ferrous iron content in soil near rice roots were monitored throughout the cultural cycle using MPN and colorimetric methods, respectively. The total iron content was evaluated in rice plant using spectrometric method. Data obtained were analyzed in relation to fertilization mode, rice growth stage and rice yield using the student’s t-test and XLSTAT 2014 statistical software. The experiment revealed that NPK + Urea and NPK + Urea + Ca + Mg + Zn fertilization, decreased significantly (p < 0.0001) the number of IRB in the soil for BOUAKE-189 rice varieties. In most pots, highest IRB densities and ferrous iron content in soil were recorded from rice tillering and flowering to maturity stages, indicating that rice plants promoted microbial processes and iron reduction in soil. From the study, the NPK + Urea amendment decreased significantly ferrous iron content (p < 0.0001) in soil near BOUAKE-189 and ROK-5 rice varieties roots relatively to control pots. However, NPK + Urea + Ca + Zn + Mg amendment increased significantly ferrous iron content (p < 0.0001) in the soil near roots, Fe accumulation in plant biomass and rice yield for the two rice varieties.