Polysulphate: a Scientific Approach to Soil Salinity

Polysulphate is a unique fertilizer made from the natural mineral polyhalite. It is the world’s only natural 4-in-1 fertilizer, providing sulfur (S), potassium (K), magnesium (Mg), and calcium (Ca), all in sulfate form. With a natural, prolonged release pattern, Polysulphate has consistently been shown to improve crop yield and quality. A quick review of the trials published on this site clearly demonstrates its benefits for a multitude of crops.

As a natural product that is simply mined, crushed, and screened, Polysulphate also boasts a very low carbon footprint. The simplicity of Polysulphate’s production process results in a carbon footprint of just 0.0029 kg CO₂ per kg of product, clearly setting it apart from other fertilizers.

Beyond these features, Polysulphate can also address critical agricultural challenges, including soil salinity and sodicity. These salt-related soil impairments can hinder crop growth but, according to ongoing, independent research carried out since the mid-2010s, Polysulphate can offer an effective solution.

What is Soil Salinity?

Saline soils have an excess of soluble salts, primarily sodium chloride (NaCl), in the soil water. This high salt concentration reduces the ability of plant roots to absorb water, even when the soil has a high moisture level, impacting plant growth and leading to lower yield and, in severe cases, crop failure.

What are Sodic Soils?

Sodic soils differ in that the sodium (Na⁺) occupies the cation exchange sites in clay particles. This disrupts the soil structure, sealing off the soil pores and preventing water and root penetration. Like salinity, sodicity reduces water uptake by plants and causes similar growth and yield problems.

Polysulphate’s Role in Tackling Sodicity and Salinity

Polysulphate contains potassium (K), magnesium (Mg), and calcium (Ca), which can replace the sodium in the soil structure, helping to restore soil health. This theory is backed up by independent laboratory and field experiments carried out by the Volcani ARO and other research institutes.

Soil Column Test

In laboratory research, soil columns were treated with a solution containing Polysulphate, and the leachate was analyzed for electrical conductivity (EC), pH, and sodium (Na), calcium (Ca), potassium (K), and magnesium (Mg) levels. These results revealed that water containing Polysulphate significantly increased sodium leaching, indicating sodium exchange had taken place in the soil.

Polysulphate and Darcy’s Test

High soil sodicity restricts water movement in the soil. Darcy’s test, which measures permeability, demonstrated that Polysulphate application significantly improved the soil hydraulic conductivity (water movement) by preventing soil structure degradation and soil pore clogging.

Field Trials Demonstrating Polysulphate’s Effectiveness

While laboratory experiments can demonstrate the theory, field trials are important to validate Polysulphate’s benefits in the field.

Polysulphate significantly reduced soil sodicity in citrus orchard.

Commercial Citrus Orchard

A field trial in a citrus orchard assessed soil sodicity by measuring the sodium adsorption ratio (SAR) of water extracted from the soil before and after the irrigation season (summer).

Polysulphate was applied to the citrus crop in a suspension at 300 kg/2,500 m² using a standard drip irrigation system, either as a single application or over five applications, with two weeks between each dose.

The results were conclusive: Polysulphate significantly reduced soil sodicity, with the best results observed with repeated applications.

Olive Orchards

Another trial in an established Olive orchard compared Polysulphate to four other soil amendments, including calcium chloride (CaCl₂), magnesium chloride (MgCl₂), sulfuric acid, and gypsum. Polysulphate and gypsum were applied to the surface, and the remaining amendments were delivered via irrigation water.

Soil samples demonstrated that Polysulphate was the most effective treatment in lowering the soil’s sodium adsorption ratio (SAR), highlighting its potential to improve soil health.

Effect of soil amendments on sodium adsorption ratio (SAR) at depth of 0-30 cm. Letters indicate significant difference (p<0.05).

Additional Benefits of Polysulphate Fertilizer

This history of ongoing, independent laboratory and field trials highlights the potential of Polysulphate as a soil amendment, as well as a multi-nutrient fertilizer. The unique properties of this polyhalite-based fertilizer mean Polysulphate has the potential to reduce soil sodicity while at the same time delivering balanced and prolonged crop nutrition.