Frequently asked questions

POLY4 is the commercial name for the Anglo American Crop Nutrient product, created from a natural mineral called polyhalite. It includes four of the six key macro nutrients that all plants need to grow: potassium, sulphur, magnesium and calcium. Its chemical formula is K₂SO₄MgSO₄2CaSO₄2H₂O.

POLY4’s four macro nutrients are 14% K₂O, 17% CaO, 6% MgO and 19% S, which are based on a 90% polyhalite content of the ore body.

The declared content is based on a 90% polyhalite content of the ore body. The remaining 10% is anhydrite, magnesite, kieserite, hexahydrite, szaibelyite, gypsum, halite, mica and syngenite.

The label-declared analysis of a fertilizer is the minimum content of its nutrients. It is most commonly expressed as a percentage by weight. Nutrient value is expressed in units to allow fair comparison of nutrient content between different fertilizers.

The elemental K, Ca, Mg, S, H and O composition of pure polyhalite is 12.9, 13.3, 4, 21.2, 0.7 and 47.8.

POLY4 is made from polyhalite, a natural mineral found underground. After extensive testing, we indicated that the typical composition of our product will be 90% polyhalite.

Potassium plays a critical role in: activation of different enzymes; maintenance of optimum cell pH; influencing photosynthesis, and transport of sugar, nutrients and water; synthesis of proteins and starch; and improving crop quality.

Magnesium enhances a broad spectrum nutrient uptake; it is constituent of chlorophyll and so affects photosynthesis; it is critical for energy transfer reactions influencing respiration.

Calcium influences nitrogen metabolism and potassium uptake; cell elongation and division; the transport of carbohydrates and nutrients thus encouraging root growth and crop quality.

Sulphur is a constituent of three amino acids and coenzyme A thus it influences protein and fatty acid synthesis; it maintains an optimum N and S ratio and protein content; it also influences chlorophyll and ferredoxin content prompting nitrite and sulphate reduction and subsequently crop quality.

POLY4 provides sulphur in sulphate form making it available to the plants. Our crop trials have shown that the sulphur supplied improves yield and quality. We have also seen a soil nutrient legacy from POLY4 making sulphur available for the next season’s crops. Sulphate is a plant nutrient and has no toxic impact on the environment or other deleterious implications for soil or the plant itself.

Our specification offers a typical halite content of 3.07% with 1.2% of sodium content and 1.9% of the average content of Cl-.

POLY4 does not contain heavy metals. It is a natural material that contains beneficial elements such as boron, cobalt, selenium, strontium, copper, iron, manganese, molybdenum, zinc and sodium. Testing of POLY4 for the presence of aluminium, vanadium, thallium, beryllium and silver resulted in nil detections.

The structure of polyhalite is crystalline, and, in solution, cations are K+, Mg2+ and Ca2+ whilst the anion is SO₄ 2-. Sulphur being the SO₄ 2- anion is the form in which plants absorb it. All nutrients in POLY4 are available for immediate plant root uptake.

To sustain crop yield and quality, a minimum level of nutrient status needs to be maintained in the soil. Our agronomic trials’ data shows that POLY4’s nutrients (potassium, magnesium, calcium and sulphur) become available over time, which more closely meets the nutrient uptake requirements of the plant.

All forms of POLY4 adhere to the same minimum nutrient content specification.

Both, POLY4 and gypsum, contain calcium and sulphate-sulphur, though only 27% of POLY4 components are the same as in gypsum.

Our trial results show the value of calcium (Ca) and sulphur (S) for soil structure and crop nutrition. Data also indicates that POLY4 typically delivers improved uptake of Ca and S.

POLY4 is approximately five times more soluble than gypsum. If POLY4 is applied at agronomically advisable rates and under normal soil conditions, precipitation will not occur.

Repeated field testing indicates crops do not suffer a lack of phosphorus availability. On the contrary, our crop trial results show evidence for improved nutrient capture.

POLY4 granules will have a minimum crush strength of 6.5 kilograms of force.

Critical relative humidity (CRH) is the value of the relative humidity of the surrounding air above which a fertilizer will absorb moisture and below which it does not absorb moisture. This is important in preventing fertilizer from caking that makes it difficult to handle or use. Uncoated POLY4 has a CRH of 70%. This is similar to other products such as MOP (CRH of 72%).

POLY4 has a solubility of 27 g L^-1 at 25°C. With this solubility, POLY4 effectively delivers K₂O, MgO, CaO and S at commercially-required rates.

Since POLY4 is a mineral, dissolution results in simultaneous nutrient release. Dissolution rate characterises the transition of a solid fertilizer into a solution. This rate is largely governed by physical parameters controlled during the patented granulation process. The result is a dissolution rate that favours provision of nutrients supporting plant growth throughout the growing season.

Potash is a generic name for a range of potassium-bearing minerals and industrial products, which include muriate of potash (K₂O), potassium sulphate (K₂SO₄) and polyhalite (K₂Ca2Mg(SO₄)4·2(H₂O)). POLY4 differs from most potash fertilizers because it is produced from a natural mineral with no chemical processing. This supports POLY4’s organic registration and maintains its micro nutrient component. Further, the primary difference from muriate of potash (KCl) is the low chloride nature of POLY4.

Results from seven independent laboratories using contemporary Jackson method show a POLY4 salt index of 76 compared to 130 for MOP, 97 for SOP and 80 for SOP-M.

Historical research has indicated that the nutrients such as calcium and magnesium can be beneficial particularly to the physical and chemical properties of the soil. The presence of these nutrients within POLY4 means that the soil environment can benefit in one season and over time.

POLY4 delivers sulphur in the sulphate form. This soluble cation does not accumulate in the soil, but moves out with water drainage. An independent review of the environmental risk concluded that POLY4 does not present a risk.

POLY4 is a pH neutral fertilizer and does not affect soil pH regardless of the quantity applied. Using POLY4 as a component of fertilizer plans may result in reduction of acidifying effects from other nutrient sources such as ammonium sulphate.

Testing results demonstrate that POLY4 has a sufficient crush strength (6.5 kgf) throughout the manufacturing, handling and loading process. Our product is of premium quality, which means that it has a low caking tendency with a CRH of 70% and is compatible with other NPK fertilizers. A farmer, who gets the product at the end of the supply chain, will receive POLY4 granules with a long shelf life, durable and suitable for mechanical spreading up to 36m widths.

No. POLY4 is not made using chemical synthesised materials unlike nitrogen fertilizers that are chemically manufactured, eg, urea or ammonium nitrate. Since POLY4 is formed from natural materials, there is almost zero chance of it catching fire.

Independent providers have ratified that POLY4 can be used as an ingredient in dry blends, compacted and steam granulated NPK alongside urea, DAP, rock phosphate, ammonium nitrate and MOP, being both physically and chemically compatible. Importantly, POLY4 blends can meet industry’s shelf life expectations.

IFDC testing validates POLY4’s compatibility across dry blend, complex, complex/compound NPK production. The high density of nutrients contained in POLY4, makes it an ideal feedstock to transform standard NPK blends into NPK+ blends supporting balanced fertilization globally.

The measure used in mineral processing is the abrasion index (AI). Polyhalite used for POLY4 production has measured an AI value of 0.002, which is two orders of magnitude lower than most common materials. This is because quartz or silica/silicates are essentially absent from polyhalite.

We recommend that farmers’ fertilizer plans are provided by qualified advisors. The best agronomic and economic solutions maximise the value of each component of a fertilizer plan, whether supplied as a straight component, in blends or complex compounds.

Potassium chloride or MOP is a single nutrient source rated at 60% K₂O, whilst POLY4 is a multi-nutrient source with rated nutrient contents of 14% K₂O, 6% MgO, 17% CaO and 19% S.

Through extensive testing, we have validated globally that, through the K rate response curve, using less K in POLY4 straight applications and in blends delivers better results. Crop fertilizer plans will be delivering not just potassium (K₂O) but also other macro nutrients such as magnesium and sulphur. Therefore, it is not an equitable comparison to compare MOP and POLY4. Under these circumstances there is little difference between the weight of fertilizer required for either plan.

Uniformity of application is expressed as the coefficient of variation (CV). A lower CV means a more even distribution of a fertilizer. A CV of more than 20% generates stripes in the crop. Uneven spreading increases the cost of the crop production due to yield penalties and required corrective actions.

Spreader testing has demonstrated that POLY4 spreads at widths of both 24m and 36m. Test results ranged from a CV of 4.4 to 5.8%.