Soil testing. A pH meter testing the acidity or alkalinity of soil. Farmers and gardeners use pH meters to determine the level of acidity in soil to assess its suitability for different plants. A probe placed in the soil measures the amount of free hydrogen ions present, giving a value of acidity on a pH scale. A pH of 7 is neutral, above 7 is alkali and below 7 is acid. This meter displays a pH of 6, meaning that this is a normal (close to neutral pH) soil. For acid and alkaline soils, see E770/1091 and E770/1156.