What does soil pH actually represent? 01-14-08

On numerous occasions we have mentioned the importance of soil testing and maintaining an optimal soil pH for your lawn, garden, and landscapes. But just what is soil pH (acronym for potential hydrogen) and how is it relevant to plant health?

In the simplest terms it is a measure of relative acidity or alkalinity on a scale of 0 to 14 with 7 being neutral. When the soil pH becomes too low (acidic) or too high (alkaline) many nutrients become less soluble therefore limiting their availability to plant roots. For maximum nutrient availability a soil pH range between 5.8 – 7.0 is most desirable. A slightly acidic soil can also provide benefits in the reduction of some plant diseases.

The pH scale is a logarithmic scale, so a change of one unit represents a 10-fold difference in acidity or alkalinity. This means a soil with a pH of 5.0 is 10 times more acid than one with a pH of 6.0 and 100 times more acid than a soil with a pH of 7.0. Soil pH is affected by applications of fertilizers, rainfall, organic matter, soil texture, and soil microorganisms, so it is important to periodically take a soil sample to determine if the pH is still within a desirable range for nutrient availability, microbial activity, and good plant growth.

Published January 14, 2008

Dr. Wayne Wells is an Extension Professor and Turfgrass Specialist. His mailing address is Department of Plant and Soil Sciences, Mail Stop 9555, Mississippi State, MS 39762. [email protected]