"Salts" and the Salt Index

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andy10917
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"Salts" and the Salt Index

Post by andy10917 » September 21st, 2018, 3:33 pm

I've been waiting for a almost a decade for someone to say "What!! Epsom Salt? You want me to put SALT on my lawn??!!?" :shock: It finally got asked.

This is good reading for all, but REQUIRED reading for those of you that never took Chemistry in high school, or who slept through it and bombed the Final (but looked very well-rested)...

Inorganic elements can have a positive or negative charge. Positive and negative "ions" attract each other, and they combine into compounds. They are far more stable and may not exhibit the properties of the individual elements that make them up - for example, Chlorine is generally a gas that can easily kill you if inhaled in any significant quantity, and Sodium is a soft metal, that reacts violently and even explodes with water - even the humidity in air. The combination is Sodium Chloride - better know as "Table Salt". It is great on french fries, and behaves nothing like Sodium or Chlorine.

In nature, almost all inorganic elements combine into stable compounds known as Salts, and are stable. I repeat -- ALMOST ALL. Gypsum? Yep! Sulfate of Potash? You bet! Lime? Yessir! Urea? Uh-huh!

"Epsom Salt(s)" are nothing special. They're Magnesium Sulfate. The word SALT is just a name, and they truly are a Salt. Gypsum is Calcium Sulfate. They're all Salts.

Now, some Salts tend to be more chemically active, and when in water they separate and form ions that are more or less active. There is a chart that shows the level of activity and potential to "burn" plants and/or the microherd. Higher numbers can have a higher Salt Index Number, and lower have a reduced risk.

Salt Index Table

Epsom Salts (Magnesium Sulfate) are in the middle of the pack at 44. Calcitic Lime is in the low end at 4.7. Urea is at higher at 74.4. The worst one? Muriate of Potash ("MOP" or Potassium Chloride) at 116.2. Does anyone have an idea why I'm always pushing Sulfate of Potash (Potassium Sulfate) at 42.6 instead? Why are so many cheap fertilizers using MOP instead of SOP then? It's cheaper, that's why!!

I hope that that helps you understand why "Epsom Salt(s)" are different than Table Salt, and why we pick different Salts to minimize the risk of "burning your lawn" and heaping (possibly invisible) damage to the all-important microherd in your lawn's soil !!

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ken-n-nancy
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Re: "Salts" and the Salt Index

Post by ken-n-nancy » September 21st, 2018, 5:28 pm

Thanks, Andy, for this write-up on "salt index" as well as the fact that from a chemistry perspective, there are lots and lots of salts other than the "table salt" that we usually just call "salt."

Just in case anybody is curious, table salt (sodium chloride) has a "salt index" too, but isn't listed in the table to which Andy linked. The "salt index" of table salt is 153.8, which makes it "saltier" than any of the fertilizers listed on the table, and is a big part of why you don't ever want to put table salt or road salt on your lawn if you can avoid it!

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