Gypsum can be used as soil amendment to improve structure in clay soils, by binding small clay particles in a process called flocculation, which improves soil aeration and water movement through the soil.²  Gypsum can also  be used to provide a supplementary source of calcium and sulphur for crops during periods of high calcium demand.  The difference between the two uses is the quantity and timing of the application ¹.

Soil Structure Improvement

The ideal period for gypsum application for soil structure improvement is before planting or once the crop is removed.²

To assess if your soil will benefit from a Gypsum application, here is a checklist;

• Water puddles on the soil surface
• The soil particles slake or disperse when added to water
• The subsoil pH is lower than 5
• There is waterlogging in the soil
• A crust forms on the soil after rain or irrigation
• There is excessive cracking of the soil after rain or irrigation
• The soil contains clay that is dusty when dry
• Salt build up in the soil due to fertiliser use or saline irrigation

Apply gypsum at a time when it is appropriate to be in the field without physically damaging the soil or the crop.²

Gypsum is moderately water-soluble and moves into the soil profile with rain or irrigation along with good soil moisture levels.

As a guide, a gypsum application rate can range from 1kg to 3kg per hectare and works best when the calcium base saturation is above 60%.  Consult your agronomist or fertiliser advisor as a guide on the best rate of gypsum based on recent soil test results.

High calcium demand periods

Calcium is an important nutrient for all crops, in fruiting crops it is closely related to the quality of the crop harvested and to the quality of the fruit during storage. ³

High demand periods for calcium in crops take place when crops are actively growing and there is a lot of cell division taking place, examples include early plant establishment or during flowering and fruit set.

For orchard crops, peak calcium demand generally occurs during the cell division stage in the weeks immediately after flowering and fruit set.¹  A gypsum application  applied late winter or early spring will allow the calcium release to peak during and just after pollination when demand for calcium is high¹.

For potato crops, the application of gypsum would occur just prior to or at planting to supply additional available calcium in the soil solution around the stolon and during the hook stage of potato crop production when crop yield is determined.

As a guide, applications would be timed to match the optimum release of calcium as well as crop demand. For example, the calcium release curve of finely ground gypsum peaks about 90 days after application and then begins dropping off. ¹

When used as a supplementary calcium fertiliser, Gypsum application rates would be advised by your crop advisor or agronomist based on recent soil test results and will take into consideration the application of base fertilisers around the same time.

Gypsum has many benefits to improve soil structure and support crops during active periods of growth. Talk to your fertiliser advisor for more information about using gypsum in your crop. 

Gypsum is BioGro certified.  Gypsum for healthy crops and healthy soil.

References

Advancing Eco Agriculture blog: Nutrient Application Timing

Ohio State University, Soybean, Gypsum fact sheet

American  Society of Agronomy: calcium: improved plant health and nutrition