Gypsum is an important and common input in Wimmera farming systems, and understanding when an application is effective and efficient to ensure a response and return on investment is paramount.
Calcium sulfate, more commonly known as gypsum, is used on heavy clay soils throughout the Wimmera to help break down the clay and enhance the calcium component of soils.
A soil is said to be sodic when there is an abundance of sodium cations bound to clay particles. This causes dispersion when wet, leading to the degradation of soil structure which in turn has effects on compaction, crop emergence and root growth.
By adding gypsum to the soil, the calcium cations in the gypsum swap with the sodium cations that are bound to the clay particles helping to prevent further structural issues.
Sulphur is vital in photosynthesis and therefore sulphur deficiency is another reason why farmers might apply gypsum.
When you remove one tonne of wheat, you are also removing approximately 1.5kg of sulphur. This drastically increases with canola, where 10kg of sulphur is removed for every one tonne of grain.
This is just the amount removed in grain, plants need approximately double that for production.
For this reason many apply gypsum before canola to increase available sulphur, but is this decision a cost effective one?
Research conducted by Maurie Street at Grain Orana Alliance in NSW was unable to consistently demonstrate that additional sulphur increased yield or oil percentage in canola.
While gypsum is a relatively cheap option for sulphur compared to SOA, it still represents a significant input into the system. Therefore determining the return on investment in applying gypsum should be made.
In a study conducted in 2015 by BCG with funding from GRDC, 13 farmer paddock trials took place in the Wimmera in which a test strip was left without gypsum application.
Each paddock underwent soil tests to determine if they would be responsive for sodicity and sulphur, with the applied gypsum also analysed to determine the quality.
While 2015 was not an ideal year to be conducting response research, one site did show significant yield increase with gypsum application. This site also had a soil result showing responsiveness to both sodicity and sulphur.
At the 2016 BCG Main Field Day, Model Agronomics consultant Tim McClelland explained that even when a sulphur deficiency is identified in-crop, it is not too late to apply to mitigate any plant health issues.
He also explained that when considering applying gypsum, undertaking a soil test will enable you to make a more informed decision and consider the return on investment.
For more information about gypsum responsiveness in the Wimmera listen to Tim McClelland’s presentation from the BCG Main Field Day (linked below).
https://soundcloud.com/bcg-birchip/gypsum-management-tim-mcclelland-model-agronomics
This article was published in the Stock and Land on January 5, 2017.
