Frequently asked questions
POLY4 – nutrient content
What is POLY4?
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.
What is the specified nutrient content of POLY4?
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.
Why doesn’t the declared nutrient content of POLY4 add up to 100%?
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.
What does the average polyhalite grade of 90% mean?
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.
Why is the potassium (K) contained in POLY4 good for plants?
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.
Why is the magnesium (Mg) contained in POLY4 good for plants?
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.
Why is the calcium (Ca) contained in POLY4 good for plants?
Calcium influences nitrogen metabolism and potassium uptake; cell elongation and division; the transport of carbohydrates and nutrients thus encouraging root growth and crop quality.
Why is the sulphur (S) contained in POLY4 good for plants?
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.
Does POLY4 have too much sulphur?
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.
What are the benefits of the micro nutrients contained in POLY4?
POLY4 contains eight micro nutrients:
- Boron (B): cell division and regulation metabolism of carbohydrates;
- Copper (Cu): important for pollen tube production, cell wall structure and function as well as photosynthetic and respiratory pathways;
- Iron (Fe): an essential co-factor in a range of cellular redox reactions; important in energy transport metabolic pathways of the mitochondria and chloroplast;
- Manganese (Mn): essential for nitrate reduction and involved in the regulation photosynthetic enzymes;
- Molybdenum (Mo): essential cofactor of enzymes for the conversion of nitrate to amino acids and inorganic P to organic P;
- Selenium (Se): protects from variety of abiotic stresses such as cold, drought, desiccation, and metal stress;
- Strontium (Sr): supplements calcium uptake;
- Zinc (Zn): a component of enzymes involved in a photosynthesis, sugar and protein formation, DNA synthesis and gene regulation.
How much sodium and how much chloride is present in POLY4?
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-.
What is the heavy metal content in POLY4?
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.
POLY4 – nutrient delivery
What form are the macro nutrients delivered in POLY4?
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.
What is the nutrient release profile of POLY4?
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.
Is there a nutrient difference between various forms of POLY4: granules, micro granules, powder or crushed?
All forms of POLY4 adhere to the same minimum nutrient content specification.
Is there a risk that calcium sulphate (gypsum) is precipitated and nutrients become unavailable to a plant?
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.
Since POLY4 delivers calcium into soil, is there a risk of making calcium phosphate and thus immobilising the crop nutrient phosphorus?
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 – characteristics
What is the crush strength of POLY4 granules?
POLY4 granules will have a minimum crush strength of 6.5 kilograms of force.
What is the critical relative humidity of POLY4?
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%).
How soluble is POLY4?
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.
POLY4 – sustainability
How is POLY4 different from other forms of potash?
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.
What is POLY4’s salt index?
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.
Does POLY4 affect the soil environment, particularly the high sulphate content?
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.
Is a POLY4’s neutral pH important?
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.
Can POLY4 be used in organic farming?
Yes. POLY4 is produced from a natural mineral and certified for use in organic systems according to the UK Soil Association and Organic Farmers & Growers. Farms certified by Soil Association or Organic Farmers & Growers do not need prior approval to use POLY4. However, use requires an on-farm justification, which is verifiable at audit.
POLY4 – handling and use
How does POLY4 handle?
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.
Is POLY4 flammable?
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.
Does POLY4 blend with other fertilizer inputs? Does it work in the majority of NPK plants?
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.
How abrasive will POLY4 be on our machinery?
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.
Do I have to apply four times as much POLY4 as MOP?
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.
Can I spread POLY4 at 24m and 36m?
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%.