Abstract
Sulfide toxicity is a common disease generally associated with iron toxicity which occurs in rice fields when the Sulfate-Reducing Bacteria (SRB) produce sulfides ions in anaerobic conditions. The high quantity of sulfides ions in the soil solution upsets the mineral element balance in the rice, affects its growth and causes crop yield losses. In Burkina Faso, many rice field soils are abandoned due to sulfides toxicity. The present study was developed to evaluate the impact of subsurface drainage on SRB dynamics and activity during rice cultivation and the incidence on rice production. Twelve concrete microplots with a clay-loam soil and a rice variety susceptible to sulfides 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 SRB populations and the content of sulfides ions in the paddy soil and in soil near rice roots 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’s t-test and XLSTAT 7.5.2 statistical software. From the results obtained, the subsurface drainage did not affect significantly SRB populations (P = 0.187). However, the drainage affected significantly sulfides concentration in the soil near rice roots (P = 0.032). The concentration of sulfides (P < 0.0001) in soil near rice roots and the number of SRB (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 a low concentration of sulfides in soil near rice roots.
Highlights
Sulfur is among the most abundant elements on the Earth [1]
Many studies showed that sulfate-reducers are common in flooded soils and they are found near rice roots [8] [32]
Our study revealed that the number of Sulfate-Reducing Bacteria (SRB) in soil near rice roots increased gradually with fluctuations from the transplanting day to rice flowering and maturity stages in all the paddy microplots (Figure 4)
Summary
Sulfur is among the most abundant elements on the Earth [1]. In rice soils, S cycle has two major aspects: plant nutrition and sulfides toxicity to the plant. Sulfate-Reducing Bacteria (SRB) are ubiquitous and quantitatively important members in many ecosystems [1] [3] They constitute a group of prokaryotes with diverse morphological and metabological characteristics, able to use several low-molecolar organic compounds, including mono- and dicarboxylic aliphatic acids, alcohols, polar aromatic compounds and hydrocarbons [4]-[6]. SRB constitute a diverse group of prokaryotes with the common ability to metabolize oxidized sulfur compounds. They are universally distributed where sulfate reduction is the dominant biomineralization pathway as fens [10]-[12], estuary sediments [13]-[15]. The sulfide toxicity generally occurs in degraded paddy soils, poorly drained organic soils, and acid sulfate soils [21]
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