Understanding the effectiveness of polyhalite as a soil ameliorant compared to conventional products

Sodic soils are characterized by high concentrations of sodium (Na) on their exchange sites, with this adversely affecting the physical properties of the soil (Rengasamy and Olsson, 1991). The amelioration of soil sodicity primarily involves the replacement of exchangeable Na with Ca, as divalent Ca2+ ions promote flocculation. Thus, gypsum has been widely used to ameliorate soil sodicity by providing soluble Ca (Qadir et al., 2001). There are also new inorganic amendments available, such as polyhalite(K₂SO₄·MgSO₄·2CaSO₄·2H₂O), which is a naturally occurring multi-nutrient fertiliser that simultaneously supplies K, Mg, Ca, and S. Although most research has focused on the role of polyhalite in supplying nutrients and crop productivity (Pavuluri et al., 2017), comparatively little is known regarding its potential to ameliorate sodic soils.

Aims
The specific aims are to:
i) Evaluate the effects of different soil amendments on the chemical and physical properties of dispersive sodic soils during incubation.
ii) Assess the movement of calcium and other soluble ions through the soil profile during column leaching.
ii) Investigate changes in soil solution and leachate chemistry, including pH, electrical conductivity (EC), and major soluble ions, at different depths during progressive leaching.
Compare the effectiveness of polyhalite and gypsum in reducing soil sodicity and improving soil structure.
iv) Identify amendment strategies that enhance soil quality and provide practical recommendations for the sustainable management of dispersive sodic soils.

Methodology
A laboratory study will be conducted using complementary incubation and column leaching experiments to evaluate the effectiveness of different soil amendments for dispersive sodic soils. During the incubation experiment, amended soils will be maintained at field capacity under controlled conditions to assess changes in soil chemical and physical properties over time. The incubated soils will then be packed into columns and subjected to progressive leaching with deionised water under a controlled flow rate. Soil solution and leachate samples will be collected at predetermined intervals and analysed for pH, electrical conductivity (EC), and major soluble ions to evaluate amendment performance and calcium movement through the soil profile. The resulting data will be statistically analysed to compare the effectiveness of the different amendment treatments.

Expected outcomes
The findings are expected to identify the most effective amendment strategy for improving dispersive sodic soils and provide scientific evidence to support the use of polyhalite as a sustainable alternative or complementary amendment to gypsum. The results will contribute to the development of improved soil management practices for enhancing soil health and agricultural productivity in sodic soils.

This research was funded by Anglo American Woodsmith Limited.