Turf toughie: Soil pH versus buffer pH

Sometimes, a soils professor gets the same question tossed his way time and again. That’s when you know you have a true “turf toughie.”

Joseph R. Heckman, Ph.D., extension specialist in soil fertility in the Department of Plant Biology and Pathology at Rutgers, New Brunswick, N.J., says both students and superintendents ask this question often:

What’s the difference between soil pH and buffer pH?

While both have pH in their names, they are worlds apart. What’s your answer?

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ANSWER: “Soil pH measures soil acidity. Buffer pH is a technique to determine soil lime requirement,” Heckman explains. “Soil pH measures hydronium ion activity in the soil.”

Different methods are used to determine soil pH and buffer pH. For soil pH, the soil is mixed in simple distilled water and tested. For buffer pH, the soil is mixed in a special hazardous chemical reagent solution. “The amount of depression you get gives you a measure of the soil lime needed,” Heckman explains.

Limestone for soils is crucial in many areas of the Northeast and mid-Atlantic region.

So confusing are the two terms to students and professionals alike, that Rutgers has stopped using the term “buffer pH.” Instead, they now term it “Lime Requirement Index” on their soil tests. That makes the number easier to comprehend. Soil pH remains the preferred term for figuring acidity.