Gypsum (Calcium Sulphate)
The cheap mineral that does two very different jobs — feeds sulphur and calcium, and repairs alkaline soil.
- Composition
- 22% Calcium, 18% Sulphur
- Form
- White / grey powder or granules
- Price
- Low
- Best for
- Sulphur for oilseeds; reclaiming sodic soil
Overview
Gypsum (calcium sulphate) is not a mainstream NPK fertiliser; it is a soil amendment and a sulphur–calcium source. As a fertiliser it supplies 18% sulphur and 22% calcium — exactly what sulphur-deficient oilseeds and calcium-hungry groundnut need, at a fraction of the cost of specialised products.
Its second job is soil reclamation. On alkaline, sodic soils where sodium has ruined structure and stopped water soaking in, gypsum replaces the sodium with calcium and lets the sodium be leached out — the standard, government-supported way to bring a white, hard-crusted field back into production. The amount needed is set by a "gypsum requirement" soil test.
What it is and when to reach for it
- As a fertiliser: a cheap sulphur and calcium source for mustard and other oilseeds, and for groundnut, where calcium at the pegging zone improves pod filling.
- As an amendment: the standard treatment for alkaline/sodic soils with poor structure and high pH.
- It is not a substitute for NPK — pair it with your normal nitrogen, phosphorus and potassium plan.
How to use it well
- Sulphur for oilseeds: apply about 100–200 kg/acre as basal and mix into the soil at sowing.
- Groundnut: apply gypsum at the pegging stage (35–45 days) so calcium is in the pod zone when pegs enter the soil.
- Sodic-soil reclamation: apply the amount from a gypsum requirement test, spread evenly, incorporate, then leach with irrigation and grow a tolerant crop first.
Common mistakes
- Expecting gypsum to fix an acidic soil — it does not raise pH; that is lime’s job. Gypsum is for sodic (alkaline-sodium) soils.
- Guessing the reclamation dose instead of getting a gypsum requirement test — too little does nothing, too much wastes money.
- Treating gypsum as an NPK fertiliser and skipping nitrogen, phosphorus and potassium.
Organic alternative
Mineral gypsum + FYM
Gypsum itself is a permitted mineral input in organic systems; combine it with heavy FYM to rebuild structure on a reclaimed sodic soil.
Crops it is used on
Open a crop for its full nutrient schedule.
Common questions
What is gypsum used for in farming?
Two things: as a cheap sulphur-and-calcium fertiliser (especially for oilseeds like mustard and for groundnut), and as a soil amendment to reclaim alkaline, sodic soils by replacing harmful sodium with calcium. It supplies 18% sulphur and 22% calcium.
Does gypsum reduce soil acidity?
No. Gypsum does not raise pH, so it does not fix acidic soil — that is what agricultural lime is for. Gypsum is used on the opposite problem: alkaline, sodic soils, where it displaces sodium so it can be leached away.
How much gypsum for groundnut?
A common practice is about 100–200 kg per acre, with a key part applied at the pegging stage (around 35–45 days) so calcium is present in the pod zone when the pegs enter the soil, which improves pod filling.
Composition and doses follow ICAR / Soil Health Card guidance; prices are the notified subsidised rates for the season shown and are guidance, not a quote. A soil test for your field always beats a general rate. See our editorial policy.