Ammonium Sulphate

Ammonium sulphate ((NH4)2SO4) is a straight nitrogen-plus-sulphur fertiliser carrying 21% N as fully ammoniacal nitrogen and 24% S as sulphate. The product is water soluble, fast acting and has an acidifying effect on soils, which makes it well suited to alkaline-saline conditions and to sulphur-loving crops. It is notified under the FCO straight-fertiliser schedule.

Composition

Nutrient grade: 21% N + 24% S
N form: fully ammoniacal
S form: sulphate, immediately plant available
Appearance: fine white to off-white crystals

Mode of action

The ammonium ion is rapidly taken up by plant roots or nitrified by soil microbes to nitrate; the sulphate ion is taken up directly. The hydrogen ions released during nitrification lower soil pH in the immediate root zone, which improves nutrient availability in alkaline soils. In flooded paddy, the absence of a nitrate fraction means there is no denitrification loss, which is one reason it is preferred over Urea in waterlogged conditions (Ammonium Sulphate Paddy).

Target use and dose

Ammonium sulphate is used as a sulphur-bearing nitrogen source for oilseeds, brassicas, alliums, sugarcane and paddy on sulphur-deficient soils. It is also used as a corrective top dressing where vegetative growth has stalled because of latent sulphur deficiency, often in conjunction with Zinc Sulphate. On acidic soils it should be balanced with lime to offset further pH drop.

Safety and regulatory status

The product is non-hazardous in handling and is FCO-notified. Like other N fertilisers, it should be stored dry and away from oxidising chemicals.

References

Ammonium Sulfate. Mosaic Crop Nutrition Resource Library.
Ammonium sulfate. Wikipedia.