Polyhalite and the potassium paradox

There's more than meets the eye

My vision emphasized the importance of polyhalite, a nutrient-rich mineral containing approximately 14% potassium, 5% magnesium, 16% calcium, and 47% sulfate by weight. Convinced by the truth of my vision, I researched polyhalite to discover why it was so great for soil. When I discovered was surprising. Even though his potassium content is lower than some other products, such as potassium chloride which is nearly half potassium by weight, polyhalite offers some amazing benefits for soil.

The beneficial characteristics of polyhalite are essentially threefold. First, polyhalite consists of four macronutrients along with an entourage of beneficial trace minerals. Second, polyhalite is naturally gradual release, meaning that it delivers its ingredients over the natural lifecycle of crops and soil organisms, without harsh impacts. Third, in addition to potassium, the formula for polyhalite includes two divalent positively charged ions (magensium and calcium) which are chemically paired with the relatvely large, likewise divalent sulphate ion, with its multimple bonding sites.

Don't let the scientific sounding words confuse you, it's really quite simple. There are many small particles in soil that have negative charges. Beneficial minerals  with a positive charge (cations) can hang out around small negatively charged particles of organic matter and clay in the soil. When these ions are divalent, they can bind with one particle on one side, and another particle on the other. Think of the bonding sites on these divalent ions like hands. Polyhalite contains the divalent ions magnesium Mg2+ and calcium Ca2+. So polyhalite improves soil structure (tilth), improving the soil in various ways by allowing for better tilth aeration, water permeability, root growth and a thriving soil ecology. 

The opposite of a cation (positively charged) is an anion (negatively charged), and the anions in polysulfate are sulfate ions, which are relatively large, complex, and divalent. These can also help with soil structure by displacing monovalent sodium ions which in excess can lead to dispersion. So all in all, on both sides of its chemical balance, polyhalite helps with soil structure.

Polyhalite even contains small amounts of chloride (around 2 to 3%), which is also a micronutrient. Plants need chloride, just like people also need it, but in small amounts. Polyhalite also supplies calcium, magnesium, sulfate, and trace minerals such as boron, zinc, manganese, molybdenum, iron and copper – with nil detections of heavy metals. 

Many people ask, "Why would I use polyhalite when I can use other, cheaper sources of potassium?" Well the answer is that maybe you should use cheaper forms, while complementing these with polyhalite. As explained on this website's "Other Benefits" page, polyhalite aids in establishing a dynamic environment for soil chemistry. It is not enough to simply add nutrients like potassium, if the soil chemistry is not conducive to nutrient exchange and uptake into the roots. There are also the further issues of soil tilth and a balanced environment for healthful organisms such  as benefical fungi and other soil microbiota. And of course, polyhalite is a source of potassium in its own right.

What's more, studies have shown that polyhalite actually, somehow, seems to deliver more potassium effectively to plants than other crop nutrients with even higher percentages of potassium.

This effect has been called the "potassium paradox," a term which refers to how polyhalite Has been shown in field experiments to outperform other crop nutrients with higher potassium content, even in terms of effective delivery potassium to plants. There are several explanations for this as discussed below. It could be due to the polyhalite's benefit to the soil's ECEC, as discussed above, or to improved soil tilth, thus allowing more potassium transport to the roots. It could furthermore be related to the action of myccorhysal fungi, benefited by polyhalite, which in healthy soil stretch in networks far and wide in the soil, bringing potassium into the roots of crop plants. It could also be due to a more robust and thriving soil microbiota.

It's hard to pinpoint why polyhalite boosts the effective delivery of potassium to crop plants so much, which is why it is called the "potassim paradox." Numerous investigations, including one extensive study involving over 1,400 farms, support these observations and provide valuable insights into the effects of polyhalite as a potassium source. 

An intriguing study in this regard is “Introducing Polyhalite to Brazil: First Steps of a New Fertilizer,”  by the International Potash Institute. That study basically shows that polyhalite can deliver much more potassium than indicated by simple percentages of content. Look at the graph of their actual measurements of potassium in the soil: