Effect of Ammonium Sulfate Fertilizer Additions on Hydrogen Sulfide Toxicity
Abstract: Hydrogen sulfide (H2S) toxicity is an increasingly problematic physiological disorder reported in certain Arkansas rice (Oryza sativa L.) fields. Though the exact causes of this disorder are unknown, one contributing suspect is use of ammonium sulfate (NH4)2SO4 fertilizer. A greenhouse study was designed to investigate the physical and chemical differences in four soils in Arkansas where this disorder regularly occurs (H and HR-Y) and never has been reported (HR-N and PTRS) and to investigate the effects of different rates of (NH4)2SO4 fertilizer on those soils. According to the Mehlich 3 soil test report, few major differences were present between soils prone to H2S toxicity and those that are not. With Zn deficiencies appearing in PTRS and HR-N, several factors likely influenced this deficiency including P fertilization and flooding effects. Significant differences in soluble SO42- concentration between soil locations occurred for the first 21 days after flooding. HR-N contained significantly more SO42- and levels did not change over time. However, the other locations contained less SO42and concentrations increased, particularly during the third week. Differences between fertilizer treatments were also significant from days 2-21 after flooding. The highest treatment of (NH4)2SO4 contained the highest concentration of SO42- in solution, followed by the low treatment of (NH4)2SO4, with the 0 kg control having the lowest concentration. Concentrations of SO42- increased in each location over time. The increase in SO42- was likely caused decomposition of soil organic matter (SOM). Lack of evidence of H2S toxicity in the root examination and in the above ground biomass nutrient content, along with the soil solution results; indicate that H2S toxicity is influenced by more than the SO42- content in the soil. A combination of other factors such as Eh, microorganisms, SOM content, and environmental conditions are likely major contributors to the occurrence of H2S toxicity.