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. Please see the text below for more explanation of how this framework is being used to show trial results.

ATS Trial Locations and the TED Framework

Field trials play an important role in the testing and implementation of new agricultural products and management practices. Properly conducted trials give a good indication of a products’ performance in the soil and climatic conditions present at the trial site. However, extrapolating results from field experiments conducted at one or more locations to a larger, spatially explicit domain has been a major challenge confronting agronomic science due to the large variation in soil properties and climate governing crop response to management.

The heart of the challenge is to achieve a balance between having a spatial scheme that is so coarse that environmental variation within a technology extrapolation domain (TED) is large—leading to substantial variation in performance of a given technology, or so fine that the number of field study locations and data requirements are overwhelming. Recent advances in geographic information technologies and publicly accessible databases on soils and climate now make it possible to establish such a framework.

The framework NutrientStar uses draws heavily on the spatial scaling protocols developed to support the Global Yield Gap Atlas developed by Drs. Ken Cassman, Patricio Grassini, Justin Van Wart and the University of Nebraska.

The TED framework delineates spatial units with shared soil and climatic properties, where one might expect agronomic technologies to perform similarly, all other variables being constant. On the map above, TEDs are depicted as colored regions with trial locations indicated by icons, which are colored according to fertilizer form. These TEDs correspond to the areas of greatest rain-fed corn production in the US.

Table of ATS Studies Sorted by TED Region and Ranking

The tables below provide information about yield impacts of ESN in plot studies grouped according to the TED where the study was conducted. The NutrientStar team had to estimate which TED a study was located within, because precise GPS coordinates were not provided for most plot studies. To make this estimate, a buffer of 5 km was drawn around each study location, and the TED represented by the largest number of pixels within the buffer was chosen as the TED for that study, after eliminating all pixels without corn/soybean production. The column in the table showing the estimated TED for each study is entitled “Plurality TED”.

The confidence level for each grouping of studies is the percentage of pixels within the 5 km buffer representing the plurality TED – again, after eliminating all pixels without corn/soybean production. Confidence levels are categorized and color-coded as: high confidence (greater than 75% of pixels in buffer = green), medium confidence (greater than 50% to 75% of pixels in buffer = yellow), and low confidence (less than 50% of pixels in buffer = red).

Each TED is also ranked in terms of its importance to corn production in the Eastern US, both by number and by percent. For example, in the first set of studies conducted by Nelson et al, there is a medium confidence level that the plurality TED is accurate for the study, and that TED is ranked eighteenth in terms of area in corn production in the Eastern US, representing 1.7% of corn production. Studies that were conducted in TEDs that do not fall within the top 75% of corn-producing areas, or that were conducted in Canada, are shown in the table in grey shading. The weighted mean values for delta yield in bushels per acre and delta yield in percentage for the entire data set are also shown at the bottom of the table.

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 products 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 ft2 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.

For more information about small plot results on the effectiveness of ATS to increase yield please visit our summary page.