Northeast Research and Demonstration Farm
Soil pH is one of the most important soil characteristics of crop production. The pH is the negative logarithm of the hydrogen ion activity of a soil. For each unit increase in pH, there is a 10 times change in acidity. A pH of 5 is 10 times more acid than a pH of 6, and 100 times more acid than a pH of 7. A soil pH greater than 7 is called alkaline or basic. A soil pH less than 7 is called acidic.
Iowa State University
Pecinovsky, Kenneth and Lang, Brian, "Crop and Soil Responses to Rates of Lime" (2015). Iowa State Research Farm Progress Reports. 2192.