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Influence of Thiosulfate on Nitrification of Ammonium in Soil¹

ABSTRACT

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.

¹ Contribution no. R445 of the Saskatchewan Inst. of Pedology, Univ. of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0.

² Soil Scientist, Agriculture Canada Research Station, Lethbridge, Alberta, Canada T1J 4B1, and Professor, Dep. of Soil Science, Univ. of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0, respectively.

Received for publication July 3, 1985.