Soil Properties That Influence Hydrogen Sulfide Toxicity in Rice.

Soil Properties That Influence Hydrogen Sulfide Toxicity in Rice

Allen, J.M., Roberts, T.L., Wamishe, Y., Hardke, J.T., and Miller, D.M.

Hydrogen sulfide toxicity (HST) is a poorly understood soil disorder that occurs in rice (Oryza sativa L.). This disorder has many potential influential factors but appears to be caused by excessive sulfur and iron in the rhizosphere. This disorder occurs when sulfate is excessively reduced to hydrogen sulfide in the two-three week time after permanent flood has been established. The distinctive symptom is root blackening caused by the buildup of iron sulfide, while above-ground symptoms appear similar to nutrient deficiencies though are not correctable by fertilizer. A better understanding of the soil physical and chemical components that influence the production of hydrogen sulfide is needed in order to identify the cause of HST, and a greenhouse study was designed to investigate potential factors. Four Arkansas soils were used to represent where HST always occurs, Hunter (H) and Hickory Ridge-West (HR-W), sometimes occurs, Hickory Ridge-East (HR-E), and has never occurred, Pine Tree Research Station (PTRS). Subsamples of each location were sterilized using an autoclave to reduce microbial activity. During the course of the trial redox potential was monitored, and soil solution samples were extracted and analyzed for sulfate. Results from preliminary soil tests indicated that H, HR-W, and HR-E contained more silt and sulfur than PTRS. The ANOVA indicated a significant difference in sterilization and location occurred one week after flooding. Sterilization significantly increased the levels of sulfate from day 7-77 (p ≤ 0.0231-0.0001). From days 28-77, H and PTRS sulfate levels were higher than levels in HR-W and HR-E (p < 0.0001), which were not significantly different from each other. From days 28-77, sterile PTRS and H consistently had the highest sulfate level and unsterile soils all consistently had the lowest levels. Results from this study indicate that sulfate is not the sole driving force behind the occurrence of HST.