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Copy link Polysulphate: Can it replace KCl and Gypsum?
Learn how Polysulphate can replace or complement KCl and gypsum, offering agronomic benefits, improved soil health, and environmental sustainability.
Introduction: Embracing More Effective Fertilization Practices
As agriculture evolves, the search for more effective, sustainable, and economically viable fertilizers becomes more pressing. Potassium chloride (KCl) and gypsum have long been popular as fertilizers and, often used in complementary ways to manage soil fertility and soil salinity. While these two products serve different purposes, they are frequently linked by their impact on soil health, particularly in the context of salinity management and nutrient balance. KCl provides potassium but lacks the calcium (Ca) and sulfur (S) that gypsum supplies. However, Polysulphate—a naturally occurring mineral form of polyhalite—has emerged as a highly effective and multi-nutrient alternative or even complementary solution as both a nutrient source and soil amendment. By offering a combination of potassium (K), sulfur (S), calcium (Ca), and magnesium (Mg), Polysulphate addresses a variety of agronomic needs while maintaining environmental sensitivity.
What Are KCl, Gypsum, and Polysulphate and How Are They Different?
- KCl (Potassium Chloride): A common potassium fertilizer, KCl also provides chloride, which can be harmful to sensitive crops while contributing to soil salinity.
- Gypsum: A soil amendment that supplies calcium and sulfur, gypsum is often used to improve soil structure and mitigate salinity but lacks potassium and magnesium.
- Polysulphate: A multi-nutrient fertilizer that offers potassium, sulfur, calcium, and magnesium in a low-chloride, low-salinity form, Polysulphate supports both nutrient availability and soil health.
What Is KCl?
Potassium chloride (KCl), for good reason, is one of the most widely used fertilizers globally, providing potassium to crops. While KCl is effective and practical, it also introduces chloride into the soil. While it benefits crops that require chloride, it can be toxic to certain crops, such as potatoes and lettuce. It can also contribute to soil salinity, harming sensitive plants and potentially degrading soil health. KCl also lacks vital nutrients like calcium (Ca), sulfur (S), and magnesium (Mg), which are essential for optimal crop development.
What Is Gypsum?
Gypsum (calcium sulfate dihydrate, CaSO₄·2H₂O) is commonly applied to soils with high sodium content or salinity. It provides calcium and sulfur, improving soil structure, water infiltration, and root development. However, gypsum does not supply potassium or magnesium, which are equally important for crop growth.
What Is Polysulphate (Polyhalite)?
Polysulphate is a naturally occurring mineral fertilizer derived from polyhalite, containing potassium (K), sulfur (S), calcium (Ca), and magnesium (Mg) in a low-salt, low-chloride, and gradually released form, which enhances nutrient uptake over time. Unlike KCl, Polysulphate’s low salinity index makes it an ideal choice for a wide range of crops. It improves soil health and nutrient availability while reducing environmental impact.
Why Consider Polysulphate Over KCl or Gypsum?
While KCl and gypsum are often used together in agriculture to address potassium and calcium needs, Polysulphate can sometimes replace both fertilizers or complement existing practices. Polysulphate offers a balanced, low-chloride solution, providing potassium without the risks associated with chloride. In addition, it supplies calcium and magnesium in a naturally occurring sulfate form, which enhances soil structure and nutrient uptake.
Unlike gypsum, which only provides calcium and sulfur, Polysulphate also delivers magnesium and potassium. Or in the case of PKplus, a Polysulphate-based fertilizer, it contains phosphorus, potassium, sulfur, magnesium and calcium. This natural multi-nutrient profile helps mitigate salinity while improving soil structure, making it a more efficient, environmentally friendly option. Furthermore, Polysulphate’s lower application rates reduce both handling and transportation costs, making it a cost-effective solution for soil health and nutrient management.
Polysulphate As a Nutrient Source
Polysulphate vs KCl: A More Efficient Potassium Source
KCl is commonly used to provide potassium, but its chloride content can damage sensitive crops and soil. In contrast, Polysulphate offers potassium in the sulfate form. For example, in cotton trials, Polysulphate led to a 20% increase in yield when applied at lower rates than KCl. Polysulphate’s magnesium and calcium content also improves soil structure, enhancing water infiltration and overall plant health. Polysulphate is a comprehensive nutrient source that not only provides potassium but also adds calcium, magnesium, and sulfur. A study found that Polysulphate applied at 200 lbs/A could provide 100% of the sulfur (S), calcium (Ca), and magnesium (Mg), and up to 100% of the potassium (K), depending on soil levels. This makes it a balanced, all-in-one fertilizer. In comparison, gypsum contains about 23% calcium, while Polysulphate contains 12.2%, making it a more well-rounded fertilizer.
Polysulphate vs. Gypsum: A Better Approach for Soil Amelioration
Gypsum is commonly used to improve soil structure and reduce sodium levels. While Polysulphate also helps reduce the Sodium Adsorption Ratio (SAR) and improve soil structure, it does so more efficiently at lower application rates, making it a more cost-effective solution. Research has shown that Polysulphate performs similarly to gypsum in reducing SAR but requires less material to achieve the same or better results. Its higher solubility and magnesium content make Polysulphate more effective at displacing sodium from soil exchange sites, mitigating salinity issues, and enhancing soil health. In addition to calcium and sulfur, Polysulphate also provides magnesium and potassium, making it a more comprehensive soil amendment compared to gypsum, which only provides calcium and sulfur. These additional nutrients contribute to better water infiltration, improved root development, and overall crop health, with the added benefit of reducing environmental impact.
What Does Research Say About Polysulphate’s Effectiveness?
Increased Wheat Yield and Protein Content
Research in Spain demonstrated that using Polysulphate instead of KCl and iron sulfate increased wheat yield, protein content, and net income, highlighting Polysulphate’s ability to deliver multiple nutrients in one application.
Higher Yields and Lower Rates in Peanuts
Polysulphate shows comparable performance to gypsum in peanuts, offering a dependable and cost-effective approach to maximize yield. Polysulphate’s lower application rates could also lead to significant cost savings compared to gypsum.
Improved Cotton Yields: In trials, Polysulphate has shown a 20% increase in cotton yield over the control, even at lower application rates compared to KCl. This is due to the synergistic effect of calcium and magnesium displacing potassium in the soil, making more potassium available to plants.
More Tools in the Toolbox for Effective Farming
Polysulphate offers farmers a versatile tool that can replace or complement KCl and gypsum. It reduces the risk of soil salinity, improves soil health, and provides key nutrients. Depending on soil type and crop needs, Polysulphate can be used alone or in combination with KCl to improve both agronomic and economic outcomes. By adding Polysulphate to your fertilization strategy, you gain the flexibility to make more informed and effective decisions that benefit crop yield and profitability.
Sources:
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Barbier, A. L. (2015). Characterization and evaluation of Polyhalite used as a multi-nutritional fertilizer for maize (Zea mays L.). Doctoral dissertation, University of Florida.
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IPPotash Publications EIFC-419
