What the Heck is pH?


Remember the high school science class? No, neither do I, but if we were paying attention, we would have learned about the “litmus test.”

Here’s how it went, I’m told. First, you dip a piece of litmus paper into a solution, and it turns color…either red or blue. If the paper turns red, then the solution is acidic. If it’s blue, it’s “basic” or alkaline. If you’re interested in what litmus paper is, I think it’s made from lichens. I could go into that a little deeper, but I’m not that interested. If you are, either Google it or send me a message.

The critical point is that it tells you if the solution is acidic or alkaline. Chemists call the range between acidic and alkaline “pH.” 

The term “pH” was first described by Danish biochemist Søren Peter Lauritz Sørensen in 1909. The o with the slash is called a “minuscule” by the way, and that’s all I know about it

pH is an abbreviation for “power of hydrogen” where “p” is short for the German word for power (potenz), and H is the element symbol for hydrogen. Why a Danish scientist used a German word is Greek to me, but he was a scientist, and I’m not, so I’ll just go with the flow. The H is capitalized because it is standard to capitalize element symbols. So now you understand about as much as I do.

Chemists and soil scientists have assigned a number to the pH test, ranging from 0 (highly acidic) to 14 (highly alkaline).

As I’ve said in other blogs before, soil is made up of living and non-living materials, both inorganic and organic.  This melange of components creates some complicated chemistry. The pH designation and number are considered a “master variable” in soil science.

If I (or you, as the case may be) change the pH of a soil, the process can change biological, biochemical, and chemical processes in the soil and the interaction of those processes.

And here’s how it affects gardeners and farmers.

Let’s use phosphorus as an example. As most gardeners know, phosphorus is one of the three major nutrients that plants need. The other two are nitrogen and potassium. When you buy fertilizer, the law requires that each container on the bag provides the percentage of these three chemicals…nitrogen (N), phosphorus (P) and potassium (K), or NPK.

Phosphorus is an excellent example of how pH can help or prevent plants from taking up nutrients in the soil. Phosphorus is essential to a plant. It plays a role in photosynthesis, respiration, energy storage and transfer, cell division, cell enlargement, and several other processes in plants. If the pH of the soil is between 5.5 (somewhat acidic) and 8.5 (slightly alkaline), plants can take in phosphorus.

But if the pH is outside those levels (lower than 5.5 on the acidic side or higher than 8.5 on the alkaline side), the phosphorus interacts with other soil minerals like iron oxides and carbonates. This interaction then locks up the phosphorus and make it unavailable to plants.

 There is a “Goldilocks Zone” where the pH is just right. That range is between 6.5 and 7.5. This is the range in which most plants can access the nutrients they need.

How do you find out your pH? Get a soil test done. Here’s where you can go:

Texas A&M Soil Testing Lab

LSU Soil Testing

Mississippi State Soil Testing

Alabama Extension Soil Testing Lab

University of Florida Soil Testing Lab

More articles you might like:

Soil-The Living Layer of Earth

The World Under Our Feet

The Soil Food Web

Making Your Soil Fertile

What Is Soil? It’s Not Just Dirt!

Interview with a Soil Scientist

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