What We Know And Don’t Know About Ammonium Thiosulfate

Ammonium thiosulfate (ATS) is commonly added to liquid nitrogen (N) solutions to provide sulfur (S) to crop plants. Sulfur response trials have shown ATS to be an effective S fertilizer, however, thiosulfate and its first breakdown product, tetrathionate, are not utilized by plants. ATS can inhibit germination, hence it is not recommended for in-furrow placement. ATS can also damage plant roots.

Eventually tetrathionate is converted to sulfate, which is the form of S taken up by plants. Complete conversion of thiosulfate to sulfate may take 1-4+ weeks at temperatures typically encountered at planting and sidedressing time. Considerable variation in conversion rate exists among soils, but the soil factors affecting conversion have not been well identified. Even though sulfate availability is delayed with ATS, is should not be considered a “slow-release” fertilizer because sulfate, thiosulfate, and tetrathionate are all mobile in soil. Thus, leaching losses are expected to be a concern with applications of ATS well before planting.

In addition to providing S, ATS can also reduce ammonia volatilization by delaying urea hydrolysis. ATS also slows nitrification, the conversion of ammonium to nitrate, which can reduce loss of nitrate to the air and water. However, the inhibitory properties of ATS are not considered as good as products specifically sold to target urea hydrolysis and nitrification, such as NBPT or nitrapyrin.

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