Gypsum vs Elemental Sulfur & Pick the Right Amendment, and the Right Tonnage

It uses the USDA Agriculture Handbook 60 gypsum-requirement equation. The gypsum requirement in milliequivalents per 100 g of soil is (initial ESP − target ESP) ÷ 100 × the cation-exchange capacity. That is converted to tonnes of pure gypsum per hectare by multiplying by the gypsum equivalent weight, the reclamation depth and the soil bulk density. Elemental sulfur and sulfuric acid rates follow from gypsum-equivalence factors.

Relative to pure gypsum (factor 1.00), the calculator uses elemental sulfur 0.19 and sulfuric acid 0.61. Because sulfur is far more concentrated in acidity, only about 0.19 tonnes of elemental sulfur replaces one tonne of gypsum — but it must first oxidise, and it only works where free lime supplies the calcium.

Use gypsum when the soil lacks free lime (is non-calcareous), because elemental sulfur and acid have no calcium source to release — they acidify but cannot supply the calcium that displaces sodium. Gypsum brings its own calcium, dissolves quickly and acts within weeks. On a non-calcareous sodic soil, gypsum is the answer regardless of price.

On strongly alkaline, calcareous soils that contain free lime (calcium carbonate). There, sulfur oxidises to sulfuric acid, dissolves the native lime and frees calcium to displace sodium — effectively making your own gypsum in place. It can be cheaper per unit of effect, but you must allow several months for microbial oxidation, which needs warmth and moisture.

Because speed and cost both matter. On a calcareous soil sulfur is viable, but if at your prices gypsum costs less or you cannot wait the months sulfur needs to oxidise, gypsum wins on cost-and-speed. The tool compares the costs you enter and only recommends sulfur when it is both viable and the cheaper route.

Gypsum is soluble and acts within roughly 2 months; sulfuric acid is effectively immediate (about 1 weeks) but hazardous to handle; elemental sulfur needs about 9 months because it must be microbially oxidised to sulfate before it does anything. The ESP-decline timeline in the tool shows these different speeds side by side.

ESP is the exchangeable-sodium percentage — the fraction of the soil's cation-exchange sites held by sodium. A soil is generally classed as sodic above about 15% ESP. Most reclamation aims to bring ESP down to around 10% or below, which restores structure and infiltration. Enter your measured ESP and the target you want to reach.

Yes. Commercial gypsum, sulfur and acid are not 100% pure, so the tool divides the theoretical rate by each amendment's purity fraction to give the actual tonnes you must apply. Lower purity means more product per hectare, which the cost comparison then reflects.

If your soil has no free lime, apply gypsum whatever the pH. If it is calcareous and strongly alkaline (pH about 8 or above), elemental sulfur becomes a genuine option and may be cheaper — provided you can wait for it to oxidise. At moderate pH with free lime, gypsum is still the faster, lower-risk choice. The tool encodes exactly this decision and names the winner.

Because the requirement scales with the mass of soil you are treating, and that mass is the product of depth, bulk density and area. Doubling the reclamation depth roughly doubles the tonnes of amendment, since there is twice as much sodium-laden soil to treat. The depth and bulk-density inputs let you size this accurately.

No — it sizes the chemical amendment, which is one part of reclamation. You still need good-quality leaching water to flush the displaced sodium below the root zone, adequate drainage, and often organic matter and a tolerant first crop. Use the tonnage and cost here to budget and choose the amendment, then build the full leaching-and-drainage plan around it.