Gypsum (calcium sulphate) is a very economical source of both calcium and sulphur. The sulphur in the form of sulphate is readily absorbed by the plant.
Application rates will vary according to nutrients already present in the soil and a soil test to check for all nutrient requirements is highly recommended. However, 0.5 to 1 t/ha is the average usage. Up to 5 t/ha is recommended for a soil conditioning effect on clay soils, especially if canola is to be followed by a cereal crop the next year.
Broadcasting fine grade gypsum at a rate as low as 2.5 t/ha usually prevents clay dispersion in the short term in marginally sodic to sodic clay soils, assuming a water application rate of up to 10 mm/h (equivalent to moderately intense rain). Higher application rates are needed to prevent clay dispersion under the following circumstances:
- coarse grade gypsum is being used; or
- a longer term effect is required;
- the soil is highly sodic; or
- the water application rate is greater than 10 mm/li (increasing the water application rate decreases the time available for dissolving gypsum).
Broadcast rates of 2.5-5 t/ha usually give successful results although higher rates can be economic, particularly for high value crops or where cheap gypsum is available from a local source.
If gypsum is applied in the irrigation water, a practical rate is 850 kg/ML. At this rate an irrigation of 100 mm of water applies 0.85 t/ha. A gypsum concentration of 850 kg/ML is approximately equivalent to that obtained from broadcasting fine grade gypsum at 2.5 t/ha, and applying water at a rate of 10 mm/ha.
Solution grade aerial spraying applications have seen gypsum applied from 200kg/ha to 400kg/ha.
Examples of Gypsum Application Rate:
( dependent on prevailing soil conditions, a soil test is recommended)
Canola – general application rates range between 0.5 to 1 t/ha. However tests have proven on some soils, plant yield increases with increases gypsum rates up to 10 t/ha.
Lucerne – 0.4 to ha after every third cut can improves lucerne productivity.
Wheat – the addition of gypsum at up to 2.5 t/ha can improve yields by up to 60%.
Chickpea – up to 2.5t/ha. Gypsum application can double yields.
Faba Bean – 2.5 to 10t/ha of gypsum. Rates of 2.5t/ha can yield up to 40% more.
Rice – Gypsum application rates of 2t.ha can increase yields around 15%. Don’t not use more than 2.5t/ha on rice as heavy applications fo gypsum increase subsoil permeability, thereby increasing water use and addition of water to the watertable.
Corn – up to 8t/ha can improve yields by 9%.
Potatoes – 5 t/ha or more of gypsum have been used. Gypsum is preferred over lime for potatoes grown in acid soils so that scab may be controlled.
Sodic Soils – A guide to gypsum application rates with respect to measured soil exchangeable sodium percentage (ESP):
5>ESP ESP>10 = 5 t/ha
Land Rehabilitation Work – gypsum has been applied at rates of up to 10 tonne per ha.
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