Dynamics and Activity of Iron-Reducing Bacterial Populations in a West African Rice Paddy Soil under Subsurface Drainage: Case Study of Kamboinse in Burkina Faso

Abstract

Iron toxicity is one of the main edaphic constraints that hamper rice production in West African savanna and forest lowlands. Although chemical reduction processes of various types of pedogenic iron oxides could not be underestimated, the bulk of these processes can be ascribed to the specific activity of Iron-Reducing Bacteria (IRB). The reducing conditions of waterlogged lowland soils boost iron toxicity through the reduction of almost all iron into ferrous form (Fe 2+), which can cause disorder in rice plant and crop yield losses. Aiming to contribute at the improvement of rice yield in Africa, an experiment was developed to evaluate the impact of subsurface drainage on IRB dynamics and activity during rice cultivation. Twelve concrete microplots with a clay-loam soil and a rice variety susceptible to iron toxicity (FKR 19) were used for the experiment. Soil in microplots was drained for 7 days (P1), 14 days (P2), and 21 days (P3), respectively. Control (T) microplots without drainage were prepared similarly. The evolution of IRB populations and the content of ferrous iron in the paddy soil and in soil near rice root were monitored throughout the cultural cycle using MPN and colorimetric methods, respectively. Data obtained were analyzed in relation to drainage frequency, rice growth stage, and rice yield using the Student t test and XLSTAT 7.5.2 statistical software. From the results obtained, the subsurface drainage reduced significantly IRB populations (p = 0.024). However, the drainage did not affect significantly ferrous iron concentration in the soil near rice roots (p = 0.708). The concentration of ferrous iron (p < * Corresponding author. C. H. Otoidobiga et al. 861 0.0001) in soil near rice roots and the number of IRB (p < 0.0001) were significantly higher during the rice tillering and maturity stages. Although no significant difference was observed for rice yield among treatments (p = 0.209), the P2 subsurface drainage showed the highest yield and the lowest concentration of ferrous iron in soil near rice roots.

Dynamics and Activity of Sulfate-Reducing Bacterial Populations in Paddy Soil under Subsurface Drainage: Case Study of Kamboinse in Burkina Faso

“…Experiments were performed on the experimental site of the International Institute for Water and Environmental Engineering (2iE) from August to December 2011. The physical and chemical properties of the soil used in the experiments were described in our previous report [25].…”

“…Experiments were carried out as previously described by Otoidobiga et al [25] and Keïta [26]. Twelve microplots were constructed in reinforced concrete to prevent cracks due to temperature changes following the alternation of the rainy and the dry seasons.…”

“…The design was intended to improve circulation of water and oxygen within the rice roots zone. Microplots were filled with the clay-loam soil described above [25], and then flooded for 1 week. After the flooding period of soil, two 15-day-old plants of FKR 19 rice were transplanted at 20 cm hill intervals.…”

“…The density of SRB populations and the sulfides concentration in drained microplots could also be explained by heterogeneous distribution of oxygen through the drainage system leading to the formation of anoxic compartments [25]. A lack of oxygenation of such microsites in drained microplots may promote the SRB population survival [49] and the sulfides production [50].…”

“…To eliminate excess sulfides in soil through water management, concrete microplots were constructed, filled with a clay-loam soil and water was drained periodically during rice, as described previously [25]. The Sulfate-Reducing Bacterial (SRB) populations' density and sulfides content in the paddy soil were monitored during the cultural cycle of FKR 19 rice variety.…”