Sulphur sits alongside nitrogen, phosphorus and potassium as an essential crop nutrient — vital for protein synthesis, enzyme activity, chlorophyll formation and the oil content of seeds. As sulphur deficiency spreads across farmland worldwide, fertiliser demand is growing. The two grades farmers and distributors weigh up are elemental sulphur and bentonite sulphur.
Why sulphur matters in agriculture
Reduced atmospheric sulphur deposition and higher-yield cropping have made sulphur deficiency increasingly common. Deficient crops show pale young leaves, thin stems and reduced yield and quality. Sulphur is particularly important for oilseeds (canola, sunflower), cereals, legumes and alliums (onion, garlic), where it drives oil content, protein and flavour. Crucially, plant roots take up sulphur only as sulphate — so any elemental sulphur must first be oxidised in the soil.
Elemental sulphur
Elemental (or "free") sulphur is pure sulphur in solid form — the lowest-cost way to add the nutrient and useful for lowering soil pH. But because plants can't use it directly, soil bacteria must oxidise it to sulphate first, and the rate depends on particle size, moisture and temperature. Fine powder oxidises quickly but is dusty, light and hard to spread evenly; coarser forms handle better but oxidise slowly and unevenly. That handling-versus-availability trade-off is exactly what bentonite sulphur was designed to solve.
Bentonite sulphur
Bentonite sulphur is a granular product — typically around 90% elemental sulphur bound with about 10% bentonite clay. The granule spreads cleanly like any other fertiliser, but once it meets soil moisture the bentonite swells and fractures the granule into fine sulphur particles. That large surface area then oxidises rapidly and evenly to plant-available sulphate. In short, you get the spreadability of a granule with the fast release of a powder — the best of both.
Side-by-side comparison
| Factor | Elemental Sulphur | Bentonite Sulphur |
|---|---|---|
| Typical composition | ~99% S | ~90% S + ~10% bentonite |
| Form | Powder / lump / prill | Granular |
| Spreadability | Dusty (powder) or uneven (lump) | Uniform; blends with NPK/urea/DAP |
| Oxidation to sulphate | Slow / uneven unless very fine | Fast and even (granule disintegrates) |
| Leaching risk | Low | Low (slow-release until oxidised) |
| Dust & handling | Dusty; harder to apply | Clean, free-flowing |
| Relative cost | Lower | Higher (added processing) |
| Best for | Bulk soil amendment, pH lowering | Precision fertiliser programmes |
How bentonite sulphur works in the soil
The mechanism is what makes bentonite sulphur effective. When the granule absorbs moisture, the clay expands and breaks it apart into micro-fine sulphur. Sulphur-oxidising bacteria then convert that sulphur to sulphate — the form roots absorb — steadily over the crop season. This gives a consistent supply while resisting leaching, because sulphur only becomes mobile once oxidised. The finer the dispersed particle, the faster the oxidation, so granule quality and sulphur particle size within the granule matter.
Application: crops, rates and timing
Start with a soil test to confirm sulphur status and pH. Bentonite sulphur is well suited to broadcast application and, because its granule size matches urea, DAP and NPK, it blends cleanly into compound fertiliser programmes without separating during handling. Apply ahead of or at planting so oxidation can supply sulphate through the growing season; because release is gradual, larger particles can also build soil sulphur reserves for the following season. Keep the product dry until application — it should stay in solid granular form until it reaches the soil.
Which should you choose?
For large-scale soil amendment or lowering soil pH where cost is the priority, elemental sulphur does the job. For precision fertiliser programmes that need even application, predictable release and easy blending, bentonite sulphur usually wins — which is why demand is growing fastest in oilseed, cereal and legume production and in blended-fertiliser markets.
Quality & sourcing
When buying, confirm the sulphur content (commonly 90%), the bentonite percentage, the granule size and hardness (it must survive handling yet disintegrate in soil), and moisture. Ask for a Certificate of Analysis and, for larger orders, third-party inspection. Consistent granules that spread and disintegrate reliably are what separate a premium grade from a cheap one.
Ambizent supplies sulphur in granular, powder, prilled, lump and bentonite grades, matched to your crop and market, with a COA on every shipment.
Frequently asked questions
What is bentonite sulphur?
Is bentonite sulphur better than elemental sulphur?
How does bentonite sulphur release sulphur to plants?
Which crops benefit most from sulphur?
What sulphur content does bentonite sulphur have?
Ambizent International Trading supplies sulphur, PVC & plasticizers, polyurethane chemicals and premium quartz sand to manufacturers in 30+ countries, with a Certificate of Analysis on every shipment. Request a quote →