Influence of Thiosulfate on Nitrification of Ammonium in Soil
1986
Janzen, H. H. | Bettany, J. R.
Ammonium thiosulfate, a common nitrogen (N) and sulfur (S) source in fluid fertilizer formulations, has been reported to inhibit soil nitrification processes. A laboratory study was established to determine the degree and persistence of the inhibitory effect and to examine the agronomic potential of thiosulfate as a nitrification inhibitor. Thiosulfate applied to the soil was rapidly oxidized with a temporary accumulation of tetrathionate. The formation of nitrate (NO⁻₃) from applied ammonium (NH⁺₄) was markedly suppressed at higher rates of applied thiosulfate. At the highest rate of thiosulfate application (100 mg S kg⁻¹), relative inhibition of NO⁻₃ production over 22 d was 55% as compared to 57% for nitrapyrin, applied at 2 mg kg⁻¹. Unlike nitrapyrin, thiosulfate inhibited the second nitrification reaction, the oxidation of nitrite (NO⁻₂) to NO⁻₃, and resulted in the accumulation of NO⁻₂ at concentrations as high as 42 mg N kg⁻¹. This accumulation of NO⁻₂ may represent a serious drawback to the use of ammonium thiosulfate as a nitrification inhibitor under some conditions since NO⁻₂ is known to be toxic at relatively low concentrations.
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