Ammonium Thiosulfate (ATS)
The geographic framework shown here delineates spatial units with shared soil and climatic properties, where one might expect agronomic tools and/or products to perform similarly, if all other farm management variables are constant. ATS trials conducted using UAN or UAN/urea are super-imposed on the framework, which we refer to as Technology Extrapolation Domains or TEDs.
ATS Trial Locations and the TED Framework
To better understand the climate and soil conditions under which these trials were performed please visit the TED framework page. There you will find the climate and soil conditions associated with each six digit TED (Technology Extrapolation Domain) as well as other areas that share those conditions.
Product Description and Mode of Action

Thiosulfate (S2O32-) fertilizers are a liquid sulfur additive than can be combined with various other fertilizer sources to satisfy plant nutrient requirements. While many fluid thiosulfate fertilizers are available, ammonium thiosulfate (ATS) is the most widely used fluid fertilizer that contains sulfur; it is composed of sulfur dioxide, elemental sulfur, and aqueous ammonia. Product examples include Kugler ATS and Thio-Sul®. Typically, ATS is mixed with urea ammonium nitrate (UAN) to produce a 28-0-0-5 fertilizer. Once applied, ATS reacts to form a byproduct (tetrathionate) that is eventually converted into sulfate, which is then available for plant uptake. In some cases, improved nitrogen (N) efficiency can be achieved simply by removal of the sulfur deficiency — i.e., if sulfur is no longer a limiting factor, the crop can better utilize N. Bands of ATS have also been shown to increase the solubility of some other micronutrients (International Plant Nutrition Institute n.d.).

ATS also seems to directly improve nitrogen fertilizer use efficiency and reduce the rate of nitrogen loss, and is advertised as such. The main mechanism is by slowing the rate of urea hydrolysis and thus reducing ammonia volatilization. This is mostly likely caused by the presence of the tetrathionate as ATS reacts and converts to sulfate.

Crops
ATS is for use with all crops for satisfaction of plant nutrient requirements.
Users
Farmers who wish to increase NUE by reducing sulfur deficiency.
Cost
Varies based on volume.
Form
ATS is a liquid sulfur additive.
Research Results from Field-Scale Strip Trials
NutrientStar reviewers found no published research results from field scale strip trials.
Research Results from Chemistry Trials

Note: Chemistry trials can provide information concerning the effectiveness of a product in laboratory and greenhouse settings but do not provide information related to a product's effectiveness in the field.

Prior to the identification of ATS, researchers found that other reduced sulfur compounds inhibited urea hydrolysis and nitrification. Thiourea inhibited urease and nitrification in early laboratory studies, and thioacetamide, phosphorus penta-sulfide, and calcium sulfide also inhibited urea hydrolysis (Malhi and Nyborg 1979). Later lab studies found that even low rates of ATS applied with UAN reduced urea hydrolysis and ammonium oxidation rates (Goos 1985). Early field microplot studies from North Dakota showed that ATS reduced ammonia losses when applied with UAN on a bare soil surface and wheat stubble, with the greatest reduction being from dribble application compared to sprayed (Fairlie and Goos 1986). For no-till corn in Pennsylvania, corn yield, ear-leaf N, and total N uptake increased with broadcast UAN+ATS compared to UAN alone (Fox and Piekielek 1987).

ATS may also reduce nitrification-related N loss, as it oxidizes into sulfuric acid and produces slight soil acidification in the application zone. ATS can be applied through various irrigation systems, but it is not recommended as a foliar spray due to potential crop damage (International Plant Nutrition Institute n.d.).

Research Results from Small Plots
Overview

An intensive and extensive review of the literature was completed to assess the effectiveness of ATS (Ammonium Thiosulfate) to increase yield of corn and wheat. All the research was completed on small plots. Typical plot dimensions were 5 feet wide by 60 feet long, and although plot sizes varied, none were greater than 500 square feet in size.

Corn

The average yield change measured for ATS when ATS was applied with fertilizer N was not statistically different from zero bushel/acre. ATS did not have any beneficial yield impacts.

Wheat

The average yield change measured for ATS when ATS was applied with fertilizer N was not statistically different from zero bushel/acre. ATS did not have any beneficial yield impacts.

Summary of Evidence

With the data available, and in the conditions studied, ATS failed to improve crop yield in wheat and in corn. However, since research has confirmed some potential to reduce N losses by improving sulfur and micronutrient nutrition, and by inhibiting both urease activity and nitrification, results may differ in other situations. For example, if N or S were limiting growth, ATS might have a positive yield effect. But, more data are needed before basing any programs or key decisions on this. In addition, lack of data make it impossible to determine whether there are other responses in terms of nitrogen dynamics (e.g., N losses or plant N uptake). In conclusion, unless further research proves otherwise, ATS is not likely to be highly recommended as a product for improving N use efficiency.

For more information about small plot results on the effectiveness of ATS to increase yield please visit our Research Findings Page.