Frequently asked questions
POLY4 – nutrient content
What is POLY4?
POLY4 is the commercial name for the Sirius Minerals 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%.
POLY4 – agronomic trials
How is the credibility of the POLY4 crop trial results assessed?
POLY4 trials are undertaken in partnership with independent research authorities that have their own in-house staff with a breadth of relevant experience. Currently we work with over one hundred leading agricultural universities, research institutions and commercial associates.
Have any independent crop trial results been published in academic journals or papers to support Sirius’ results?
As of April 2018, Sirius Minerals sponsored agronomic research has been published in three science journals (International Scholars Journals, Powder Technology and HortScience) with one further agronomic paper currently in press.
Much of the historic assessment of polyhalite as a fertilizer (Terelak, 1975, 1974; Panitkin, 1967; Marchesi Sociats, 1948; Lepeshkov and Shaposhnikova, 1958; Boratynski and Turyna, 1971; Fraps and Schmidt, 1932; Simrnova, 1965; Mercik, 1981) demonstrated that polyhalite could be used with equal or greater effect than other potassium fertilizers across a very broad range of important crops.
Granular polyhalite also proved an effective slow release potassium (K) fertilizer to usefully boost K uptake by ryegrass over a longer season (Mercik, 1981). Polyhalite also increased sulphur (S) uptake (Mercik, 1981), which is increasingly deficient for crops in Europe (EEA, 2012) and elsewhere. Furthermore, in deficient soils polyhalite was fully capable of providing magnesium to boost crop yields of potatoes, beets (Panitkin, 1967), and buckwheat (Boguszweski et al, 1968). Further assessments were made in the USA (Barbarick, 1989 and 1991) which confirmed equal or greater crop yields and nutrient uptake, compared to standard fertilizer. Consequently, polyhalite was accepted as a good fertilizer for K, Ca, Mg and S.
A large set of independent data demonstrates the exciting potential for POLY4. This work concentrates on the agricultural benefit to crops (Pavuluri et al, 2017; Sutradher et al, 2016; da Costa Mello et al, 2018) and the physical characteristics of POLY4 as a commercial fertilizer (Albadarin et al, 2017).
NB: Detailed references to publications are available on request.
Why would farmers want to use POLY4? Is it a low-nutrient content product?
POLY4 is a naturally-occurring, low-chloride, multi-nutrient fertilizer certified for organic use. It contains four of the six nutrients that plants need to grow and a range of valuable micro nutrients. Our product’s nutrient content (14% K2O, 6% MgO, 17% CaO and 19% S) totals 56%, which compares favourably with 60% for MOP, 57% for potassium nitrate, 67% for SOP, 45% for kieserite or 55% for gypsum. It is an effective fertilizer that allows farmers to maximise their crop yield, increase quality and improve soil structure with one simple product.
NB: Detailed references to publications are available on request.
POLY4 – market opportunity
What is the market potential for POLY4?
POLY4 has a significant market potential. The size of the market opportunity for POLY4 is framed in three key areas – as a substitute for existing products, to meet unmet market demand for high-value products and to provide premium performance.
Product substitution: POLY4’s unique multi-nutrient content enables a wide range of opportunities for existing fertilizer products substitution. In addition, the demand for multi-nutrient fertilizers continues to grow at the farm gate.
Unmet market demand: There is a need for balanced fertilization and significant unmet demand for low-chloride potassium: 32% of total potassium consumption is used on chloride-sensitive crops while supply of low-chloride potassium is only 9%. The increasing demand for key attributes of POLY4, such as its suitability for use on chloride sensitive crops and its ability to address sulphur and magnesium soil deficiencies.
Product performance: POLY4 is a premium product: it increases yield on broad-acre and high-value crops, improves crop quality and health and soil structure, which is consistently evidenced by data collected through our R&D programme. Demand for multi-nutrient fertilizers continues to grow and as the performance of POLY4 becomes more widely validated, it is expected that so will its ability to attract a premium.
Are Company’s netbacks and market prices misleading?
Sirius Minerals is a public listed company. It has obtained a Premium Listing on the London Stock Exchange and was added to the FTSE250 index. Admission to the premium listing segment of the Official List and to trading on the London Stock Exchange’s Main Market required the Company to issue a prospectus in accordance with the Prospectus Rules of the Financial Conduct Authority (FCA). The prospectus has been approved by the FCA and was made available to public.
All of the information provided in this prospectus (April 2017) and in a prospectus prepared for stage 1 financing (November 2016), including market prices, has been validated by the FCA and Allen & Overy LLP.
The pricing of the product is based upon a pricing methodology that is linked to market prices quoted by independent industry specialists, which are highly transparent and well-recognised as a benchmark for fertilizer prices.
Have freight costs for POLY4 into markets been accounted for?
Yes. The quoted prices for transportation of our product to the port of shipment, plus loading costs, are based on a variety of existing agreements and contracts in place on a CFR or FOB at Teesside port.
Does it cost more if POLY4 is included in a fertilizer plan?
POLY4 has lower application cost on a nutrient basis. Many of our trials address the value of the nutrients within POLY4 compared to current options. For example, the results of our corn trial in partnership with University of Minnesota, that compared the use of MOP and MOP + POLY4 at a ratio of 75:25 K2O as potassium and sulphur sources, showed that using MOP + POLY4 returns an extra US$247 per hectare compared to MOP while improving grain quality and increasing yield up to 15%. For some crops, such as tea we show value and economic improvement when POLY4 application meets all potassium requirements. The data collected indicates that POLY4 value is in a fertilizer plan and these plans do not require more total weight of products.
Will blenders need to install new infrastructure to work with POLY4?
No. University of Greenwich’s study of our product indicates that handling of POLY4 does not differ from other products, and there is no requirement to install new infrastructure by blenders for mechanical handling and facility requirements. POLY4 has been tested on dry blend, complex and complex/compound treatments, and covered aspects such as dumping into bins and passing around systems.
POLY4 has also been proven to handle and store effectively under similar conditions to other common fertilizer materials.