Sulphate of Potash for WA Farmers (SOPWA)

Supplying sufficient food for the rapidly growing population of the world presents one of the greatest challenges facing humanity. But it is not only the quantity of food produced that should concern us, but its nutritional quality is also important. Fertilisers offer the best means of increasing yield and of maintaining soil fertility at an adequate level to ensure that good yields and quality. Macronutrients such as nitrogen, phosphorus and potassium are the plant nutrients mostly used.

Plants also require large quantities of sulphur, calcium and magnesium and small quantities of some microelements. The intensely weathered nature of Western Australian cropping soils and the long history of potassium depletion by the farming system has resulted in an increased incidence of potassium deficiency in broadacre crops (Brennan & Bell 2013, Damon & Rengel 2007 and Wong et al. 2001). The effect of a single nutrient (like K) in fertiliser may depend upon how it is chemically combined in the fertiliser material, and this affects both yield and crop quality.

Because potassium fertilisers are obtained from natural products, they may contain substances other than K, S and Cl, and these substances may affect plant growth. Thus, choosing the right kind of potash fertiliser can be as important as applying the right amount of potash to a crop.

An Australian first controlled environmental study and broadacre field trials commenced in 2019, analysing the benefits of WA produced sulphate of potash (SOP) fertiliser.

The Australian Potash Limited SOP for WA Farmers (SOPWA) project compares commonly used muriate of potash (MOP) with SOP and investigates the full effects of both potassium sources on crop yield, quality, safety and value.  It is a research collaboration between the Western Australian No-Tillage Farmers Association (WANTFA), the University of Western Australia's Institute of Agriculture and APC.

Time and money have been invested in these trials because Australian farmers need a commercially and environmentally friendly Australian solution for improving their soils and therefore their production.  The lessons and information we extrapolate from the trials will be relevant for soils across Australia.

Broadacre Study

Farmers want to increase both the quality and quantity of their end product. They have a vested interest in helping their soils. SOP can do all of this, but it needs to be commercially viable for farmers to use it. With this in mind, SOPWA was an Australian first field trial program of SOP.

The field trials compare SOP and MOP on different broadacre crops, and in various soils.  Five trial sites, using farmers' equipment, were established at Bolgart, Tammin, Southern Cross, Kojonup and Grass Patch. The trials varied in their design and size to suit the grower's interests and capacity with their seeding equipment.

Southern Cross
Grass Patch

SOP & MOP application at the five trial sites

The field trials started during the 2019 seeding season and followed strict research methodology. To ensure complete independence, the WANTFA took charge. APC's role was to provide SOP product and finance.

We value input and inclusion, which is why we're also working with farmer groups to find an Australian price point and to find ways to supply direct to rural communities.

Plant Growth Facility Study

We understand that an essential conversation with Australian SOP end-users is about economics. Farmers need measurable results.  The second component of SOPWA is a UWA controlled environment study aimed to provide measurable results by using peer-reviewed academic research to complement the field trials.

The University of Western Australia's School of Agriculture and Environment is ranked first in Australia and "well above world standards" for its academic research. The chair and director of this school, Professor Kadambot Siddique, along with research fellow and microbiologist, Dr Zakaria Solaiman, supervised the UWA SOP Hothouse Trials.

The hothouse trials consisted of four study areas:

  • Responses of wheat and canola to rates of SOP;
  • Comparison of locally produced premium SOP and MOP on the yield and quality of cultivated grain and pasture crops;
  • Comparisons of potassium leaching of SOP and MOP; and
  • Establishment of crops - SOP effect on seed germination and seedlings' growth.

These trials quantified differences in yield and quality between SOP and MOP.  They investigated what SOP does to soil biology in comparison to MOP. This had never been done before.

UWA's Dr Zakaria Solaiman with the SOPWA hothouse trials


Brennan, R. F. and M. J. Bell (2013) Soil potassium-crop response calibration relationships and criteria for field crops grown in Australia. Crop & Pasture Science 64: 514-522.
Damon, P. M. and Z. Rengel (2007) Wheat genotypes differ in potassium efficiency under glasshouse and field conditions. Crop and Pasture Science 58: 816-825.
Wong, M. T. F., et al. (2001) A decision support system for mapping the site-specific potassium requirement of wheat in the field. Australian Journal of Experimental Agriculture 41: 655-661.