Fertilizers are responsible for over half of global food production, but there are areas in world with nutrient deficiency and other areas of nutrient excess.
Managing mineral plant nutrients requires careful application of science and skill to meet production, environmental, and social goals.
Thiosulfate (S2O32-) fertilizers are clear liquids
that provide a source of sulfur (S) and can be used in a variety of situations.
They also contain other nutrients including nitrogen (N) as ammonium (ATS),
potassium (KTS), calcium (CaTS), or magnesium (MgTS).
ATS is the most commonly used S-containing fluid
fertilizer. It is made by reaction of sulfur dioxide, elemental S, and aqueous
ammonia. Other common fluid thiosulfate fertilizers are similarly produced.
Thiosulfates are highly soluble in water and are compatible
with many other fluid fertilizers. ATS is commonly mixed with urea ammonium
nitrate (UAN) to produce a widely used fertilizer with the analysis 28-0-0-5
Formula Common Nutrient Density, pH
name content kg/L
(NH4)2S2O3 ATS 12% N; 26% S 1.34 7 to 8.5
K2S2O3 KTS 25% K2O; 17% S 1.46 7.5 to 8
CaS2O3 CaTS 6% Ca; 10% S 1.25 6.5 to 8
MgS2O3 MgTS 4% Mg; 10% S 1.23 6.5 to 7.5
After application to soil, most of the thiosulfate
quickly reacts to form tetrathionate, which is subsequently converted to
sulfate. Thiosulfate is not generally available for plant uptake until it is
converted to sulfate. In warm soils, this process is largely complete within
one to two weeks.
Molecular structure of
thiosulfate and tetrathionate
Thiosulfate is a chemical “reducing agent” and it
also produces acidity after oxidation of the S. Due to these properties, thiosulfate
molecules have unique effects on soil chemistry and biology. For example, a band
application of ATS has been shown to improve the solubility of some
micronutrients. Local guidelines should be followed for maximum rates for
placement in the seed row.
Thiosulfate can slow the rate of urea
hydrolysis…the conversion of urea to ammonium (NH4+)…and reduce loss of ammonia
(NH3) as a gas when ATS is mixed with UAN. This inhibiting effect is likely due
to the formation and presence of the intermediate tetrathionate, rather than
the thiosulfate itself. Nitrification...the conversion of NH4+ to nitrate...is
also slowed in the presence of ATS. Although the initial pH of thiosulfate
fertilizers is near neutral, thiosulfate oxidizes to form sulfuric acid and the
NH4+ in ATS will form nitric acid, thus resulting in slight soil acidification
in the application zone.
Thiosulfates may be applied through surface and
overhead irrigation systems, sprinklers, and drip irrigation. Many of them are
used in foliar sprays to provide a rapid source of plant nutrition (not
recommended with ATS).
Sulfur deficiencies are noted in crops throughout
the world. Thiosulfates are valuable fertilizer materials because they are easy
to handle and apply, require minimal safety precautions, and are compatible
with many other common fertilizers. However, these fertilizers should not be
mixed with highly acidic solutions since this will cause the decomposition of
the thiosulfate molecule and subsequent release of harmful sulfur dioxide gas.
Thiosulfate materials are used in a variety of
industrial applications. In photographic processing, they are used to bind
silver atoms present in film or paper. Sodium thiosulfate is used in water
treatment systems to remove chlorine. It is also used for gold extraction,
since it forms a strong complex with this metal in a non-toxic process.