Recent research showing the benefits of sulfur application to corn in Iowa have many folks asking questions about ammonium thiosulfate or ATS. ATS and ammonium sulfate (AMS) contain both nitrogen and sulfur, however in different amounts. AMS also differs from ATS in that all the sulfur in AMS is immediately available to plants in the sulfate form, whereas ATS contains no sulfur in the sulfate form, but changes to sulfate after application to the soil.
ATS (NH4)2S2O3 12-0-0-26S
AMS (NH4)2SO4 21-0-0-24S
ATS reacts in the soil to form tetrathionate, which is not plant available. Tetrathionate is then converted to sulfate, which is plant available. Much like nitrogen, these processes take place in the presence of bacteria as well as the appropriate soil moisture and temperatures. These processes may take one to several weeks (Camberato, 2019) but often are faster. A practical rule of thumb is that about one-half becomes plant-available within a week after application to moist soil. The change to plant-available forms is far more delayed for elemental sulfur, another common sulfur source.
ATS as a fertilizer source
ATS is highly soluble and can be added to liquid nitrogen solutions. ATS should not be applied in the furrow as it will cause seedling damage, and it should not be applied as a foliar fertilizer.
ATS has nitrification-inhibitor and urease-inhibitor properties. Franzen (2017), reviewed studies looking at ATS as a nitrification inhibitor and a urease inhibitor. While ATS has measurable inhibition properties, it is not as consistent or as effective as the use of other products such as nitrapyrin and DCD, nitrification inhibitors, and NBPT (N-(n-butyl) thiophosphoric acid triamide), an urease inhibitor. It should also be noted that it takes high rates of ATS to act as an inhibitor.
ATS as a herbicide carrier
Another use of ATS is as a herbicide carrier. However, mixing ATS with herbicides is known to cause incompatibility issues leading to uneven mixing and application of herbicides. The risk of problems increases as the quantity of ATS increases (above 10%) of total solution.
Johnson et. al., (2019) conducted a study looking at the use of ATS with glyphosate and glyphosate + 2,4-D. Using ATS and burndown herbicides can cause antagonism reducing the efficacy of the herbicides as burndown products.
When using fertilizers as a herbicide carrier always read and follow label directions. Conduct a jar test to ensure the compatibility of products.
Camberato, J. 2019. What we know and don’t know about Ammonium Thiosulfate. Pest and Crop Newsletter. Purdue University.
Franzen, D.W. 2017. Nitrogen extenders and additives for field crops. SF1581. North Dakota State University.
Johnson, B., et.al. 2019. ATS and burndown herbicide treatments. Pest and Crop Newsletter. Purdue University