International trade in ammonium sulphate has a structure that follows directly from two facts established elsewhere in this series: most supply is a by-product of industry, and the product is freight-sensitive because of its low nutrient density. The result is a trade pattern that looks quite different from that of high-analysis nitrogen fertilisers.
Surplus and deficit are defined by industry, not agriculture
For most fertilisers, exporting regions are those with cheap feedstock — natural gas for nitrogen, ore bodies for phosphate and potash. For ammonium sulphate, surplus arises wherever there is large-scale caprolactam production, extensive coke-making capacity, or ammonia and sulphuric acid available at advantaged cost, whether or not local farmers want the material.
Deficit regions are defined agronomically: farming systems where sulphur deficiency has become widespread, where soils are calcareous enough that an acidifying source is beneficial, or where sulphur-hungry crops dominate.
Because these two maps are drawn from entirely different data, they overlap only by coincidence, and trade exists to reconcile them.
Trade flows are freight-limited
The nutrient-density arithmetic — 21 % N against urea’s 46 % — means that ammonium sulphate cannot absorb long-haul freight as comfortably as high-analysis products. Three consequences follow.
Regional preference. Trade tends to flow along the shortest viable route rather than to the highest-priced market, and a nearby market at a modest level frequently beats a distant one at a better level once freight is deducted.
Vessel economics. Larger parcels reduce cost per tonne, but only where the destination can discharge and store them. Port infrastructure — covered storage, discharge rate, draft — is often the real constraint on which markets can be served economically.
Backhaul sensitivity. Because freight is such a large share of delivered cost, cargoes that can use a favourably positioned vessel enjoy an advantage unrelated to production cost.
Form determines the accessible market
The article on physical forms explains why: crystalline material is unblendable with granular products. Internationally, this splits demand in two.
Markets served by compound fertiliser plants import crystal as a raw material. Markets served by bulk blending need granular or compacted product with an SGN compatible with locally used urea, DAP and potash. Markets dominated by direct application in bags need a product that survives bagging, storage in humid conditions and manual handling without caking.
A supplier whose plant naturally makes crystal can therefore reach only part of the world market unless it invests in compaction or granulation, and this processing question governs trade access more than any commercial factor.
Standards and compliance vary by destination
Fertiliser regulation is national or regional. Nutrient declaration rules, permitted tolerances, contaminant limits, labelling language, packaging requirements and registration procedures all differ. Contaminant limits in particular are set by the destination, not the origin, and a certificate acceptable in one market may not satisfy another. Compliance is a precondition of market access rather than a commercial variable, and it is properly established before shipment rather than at the border.
Seasonality and the storage problem
Demand is seasonal; by-product supply is continuous. International trade partially solves this, because northern and southern hemisphere planting seasons are offset, allowing material produced continuously in one region to find demand somewhere through more of the year. This smoothing is imperfect — storage capacity, cargo economics and quality degradation during long storage all limit it — but it is one of the structural reasons the trade exists at all.
The summary picture
Ammonium sulphate moves internationally because industrial geography and agronomic geography do not coincide; it moves over shorter distances than higher-analysis nitrogen because freight per unit of nutrient is high; it reaches only those buyers whose handling systems match its physical form; and it clears compliance regimes set entirely by the destination. Any analysis of the trade that starts from crop nitrogen demand alone will miss most of what determines where the tonnes actually go.