Ammonium sulphate is a nitrogen fertilizer that farmers often buy for its sulphur. It contains about 21% nitrogen and 24% sulphur, written as 21-0-0-24S, and it is one of the simplest ways to supply both nutrients in a single product.
This guide explains what ammonium sulphate does in the soil, which crops and soils benefit most, how the grades differ, and when urea or another nitrogen source is the better choice. If you are looking for producers and trade data instead, see our ammonium sulphate manufacturers database.
Ammonium sulphate at a glance
| Property | Value |
|---|---|
| Chemical formula | (NH4)2SO4 |
| Nitrogen (N) | About 21%, all in ammonium form |
| Sulphur (S) | About 24%, as sulphate |
| Grade written as | 21-0-0-24S |
| Common forms | Crystalline (standard), granular, compacted |
| HS code | 310221 |
| Effect on soil pH | Acidifying |
Why farmers use ammonium sulphate
It supplies sulphur as well as nitrogen
Sulphur is needed to make proteins, and crops that are short of it cannot use nitrogen well. Sulphur deficiency has become more common in many farming regions, partly because air pollution controls have cut the sulphur that used to fall in rain. Ammonium sulphate delivers sulphur in sulphate form, which plant roots can take up straight away.
The nitrogen is in ammonium form
Urea has to be converted to ammonium in the soil, and when it is left on the surface some of that nitrogen can be lost to the air as ammonia. Ammonium sulphate already contains ammonium, so surface losses of this kind are usually much smaller, especially on soils that are not strongly alkaline. This makes it useful where fertilizer cannot be worked into the soil straight after spreading.
It acidifies the soil
As soil bacteria convert ammonium to nitrate, they release acidity. Ammonium sulphate has a stronger acidifying effect per unit of nitrogen than urea or ammonium nitrate. On alkaline and calcareous soils this can help, because it can improve the availability of nutrients such as phosphorus, iron, manganese and zinc around the roots. On soils that are already acidic it means extra lime will be needed over time.
Which crops benefit most
Ammonium sulphate suits crops with a high sulphur demand, or crops grown where sulphur is short.
- Oilseed rape (canola) and mustard: among the most sulphur-hungry field crops. Sulphur affects both yield and oil content.
- Alfalfa and other forage legumes: legumes fix their own nitrogen but still need sulphur.
- Maize, wheat and other cereals: often given a sulphur-containing fertilizer in spring on light or low-organic-matter soils.
- Rice: paddy rice takes up ammonium readily, and the ammonium form avoids some of the losses that nitrate suffers in flooded soils.
- Sugarcane: a large user of ammonium sulphate in several producing countries.
- Potatoes, onions, garlic, brassicas and many vegetables: sulphur influences quality and, in onions and garlic, flavour.
- Acid-loving crops such as tea and blueberries: the acidifying effect can be an advantage.
For crop-specific programmes, see our guides to sugarcane fertilizer and nitrogen fertilizer.
Ammonium sulphate vs urea
| Ammonium sulphate | Urea | |
|---|---|---|
| Nitrogen | About 21% | 46% |
| Sulphur | About 24% | None |
| Nitrogen form | Ammonium | Amide, converted to ammonium in the soil |
| Surface volatilisation risk | Low on most soils | Higher, unless incorporated or treated |
| Acidifying effect | Strong | Moderate |
| Tonnes needed for 100 kg N | About 0.48 t | About 0.22 t |
Many growers use both: urea as the main nitrogen source and ammonium sulphate to cover the crop’s sulphur needs. Read more in our urea fertilizer guide.
Granular, crystalline and compacted grades
- Crystalline (standard): fine crystals. Good for direct application on some crops, for NPK granulation plants and for dissolving into liquid fertilizers. Usually the cheapest form.
- Granular: larger, harder particles, often 2 to 4 mm. Blends well with granular urea, DAP and MOP and spreads evenly over wide bout widths. Usually sold at a premium.
- Compacted: crystals pressed into granule-sized pieces. An alternative to true granular for blending.
If you run a bulk-blending plant, particle size is the main thing to check. Fine crystals mixed with large granules separate during handling, and the blend that reaches the field will not match the label.
Where ammonium sulphate comes from
Much of the world’s ammonium sulphate is a by-product. It is recovered when caprolactam, the raw material for nylon 6, is made, and from the gas produced when steel plants make coke. Some is made directly by reacting ammonia with sulphuric acid. Because so much supply comes from other industries, availability and price can move with nylon and steel output as well as with farm demand.
China is by far the largest exporter. It shipped 17.1 million tonnes in 2024, more than 80% of reported world exports, at an average customs value of about $149 per tonne (UN Comtrade). Our ammonium sulphate manufacturers database shows trade for every reporting country.
Other uses
- Spray adjuvant: ammonium sulphate is added to some herbicide spray tanks to counter hard water, which can reduce the effect of certain herbicides. Always follow the product label.
- Industry: food processing, water treatment and fire-retardant formulations use industrial or food grades, which have tighter purity limits than fertilizer grade.
Handling and storage
- Keep it dry and covered: it can cake in humid conditions.
- Ask about free acidity, which can corrode equipment and damage bags.
- Check compatibility before blending with other products.
- Confirm particle size and moisture in the contract and at inspection.
Buying ammonium sulphate
When you ask for a quotation, state the grade (granular, compacted or crystalline), nitrogen and sulphur minimums, maximum moisture and free acidity, quantity, packaging (bulk, big bags, or 25 or 50 kg bags), delivery port and Incoterm. Freight is a large share of the delivered cost of a low-value product, so the loading origin matters. Our guide to requesting a bulk commodity quotation explains how to set out an enquiry.
Sourcing through Agromer
Agromer has traded agricultural commodities internationally since 1985 from Saint-Avertin, France. Our core fertilizer range is urea, NPK, DAP and potash, along with organic products. Ammonium sulphate is not one of our standard lines, but you can send an enquiry with your specification and we will tell you plainly whether we can help.
Frequently asked questions
What is ammonium sulphate fertilizer used for?
It supplies nitrogen and sulphur together. Farmers use it on sulphur-demanding crops such as oilseed rape, alfalfa, onions and brassicas, on alkaline soils where its acidifying effect helps, and on rice and sugarcane.
What does 21-0-0-24S mean?
About 21% nitrogen, no phosphate, no potash and about 24% sulphur.
Is ammonium sulphate better than urea?
Neither is better in every case. Urea contains 46% nitrogen, so it is cheaper to ship and spread per unit of nitrogen. Ammonium sulphate adds sulphur, loses less nitrogen to the air when left on the surface, and acidifies the soil.
Does ammonium sulphate lower soil pH?
Yes. It is one of the most acidifying nitrogen fertilizers. That helps on alkaline soils but means acid soils will need more lime over time.
What is the difference between granular and crystalline ammonium sulphate?
Granular material has larger, harder particles that blend and spread well. Crystalline material is finer and cheaper, and suits direct application, NPK plants and liquid fertilizers.
Which country produces the most ammonium sulphate?
China is the largest exporter by far, with 17.1 million tonnes in 2024 according to UN Comtrade.