Formula used
Laboratory mode: adjusted rate equals the laboratory rate multiplied by desired depth divided by laboratory depth. Purity and moisture then increase the delivered product rate. Always confirm the laboratory basis before applying material.
ESP mode: sodium reduction equals CEC multiplied by the desired ESP change. Soil mass comes from depth, area, and bulk density. Gypsum equivalent weight converts exchange demand into pure gypsum.
Nutrient modes: net calcium or sulphur need is divided by the guaranteed nutrient fraction. Product purity and moisture corrections are then applied. Existing nutrient credits prevent duplicate nutrient recommendations.
How to use this calculator
- Select the calculation method matching your laboratory report or nutrient goal.
- Enter the treated field area and its Canadian or imperial unit.
- Add soil-test values, product analysis, drainage, water, and cost information.
- Review validation messages before relying on the calculated application rate.
- Download the report and confirm it with a qualified adviser.
Example data
| Scenario | Important inputs | Purpose |
|---|---|---|
| Laboratory recommendation | 4 t/ha, 15 cm basis, 90% purity | Adjust a laboratory rate for product quality. |
| Sodic field | ESP 20 to 10, CEC 20, 15 cm, 1.3 g/cm³ | Estimate calcium amendment for sodium replacement. |
| Sulphur nutrition | 20 kg S/ha target, 5 kg credit, 18.6% S | Estimate gypsum from crop sulphur need. |
Frequently asked questions
Does gypsum change soil pH?
Gypsum is not a liming material. It normally has little direct pH effect. Use lime recommendations when acidity correction is required.
Can gypsum fix every saline field?
No. Salinity and sodicity require different diagnoses. Gypsum mainly helps where exchangeable sodium is the problem.
Why is drainage important?
Calcium can replace sodium on soil exchange sites. The released sodium must then move downward. Poor drainage can stop that removal process.
Why adjust for purity?
Commercial products may contain less than pure calcium sulphate. Lower purity requires more delivered material. Use the supplier's current guaranteed analysis.
Why include moisture?
Wet material contains less dry gypsum per tonne. Moisture correction estimates the as-received delivery rate. Skip it when purity is already as received.
What is ESP?
ESP means exchangeable sodium percentage. It describes sodium occupying soil exchange capacity. Laboratory methods and interpretations can vary.
What is SAR?
SAR compares sodium with calcium and magnesium in solution. It supports sodicity screening. Use laboratory guidance for final treatment decisions.
Can gypsum supply crop sulphur?
Yes, suitable gypsum can provide sulphur and calcium. Nutrient availability depends on product quality and conditions. Credit all other nutrient sources first.
Should large rates be split?
Large rates may exceed spreader capacity or incorporation practicality. Staged applications can improve logistics. Confirm the treatment programme professionally.
Are tonnes and short tons identical?
No. A metric tonne equals 1,000 kilograms. A US short ton equals 2,000 pounds.
Is this a legal fertilizer recommendation?
No. This tool provides a planning estimate only. Follow laboratory, provincial, supplier, environmental, and professional requirements.