Updated: Sep 6, 2018
pH is defined as the negative log of the hydrogen ion (H+) concentration on a scale of 0 to 14. The neutral point is 7, less than 7 is acidic and greater than 7 is alkaline or basic. The acidification of soils is the result of natural soil processes and is enhanced by cropping and crop removal, and by use of acid forming fertilizers.
The pH of the soil strongly influences on the availability of essential plant nutrients. In mineral soils the optimal pH range is 5.5 to 6.5 and in organic soils the optimal range is 5.4 to 6.0. If the pH is below or above this range, the availability of nutrients either declines, leading to deficiencies, or increases, leading to potential toxicities.
Availability of soil nutrients is affected by changes in soil pH in different ways. Most decrease in availability as the pH declines, while some, such as iron increase in availability. At a neutral pH of 7, macronutrients are highly available, however micronutrients, such as iron, are less available in the soil.