Skip to main content

Competency Area 5: Soil pH and Liming

PO 39. Describe how soil pH affects the availability of each nutrient.

Soil pH affects nutrient availability by changing the form of the nutrient in the soil.  Adjusting soil pH to a recommended value can increase the availability of important nutrients.  Plants usually grow well at pH values above 5.5.  Soil pH of 6.5 is usually considered optimum for nutrient availability.

Lower pH increases the solubility of Al, Mn, and Fe, which are toxic to plants in excess.  A critical effect of excess soluble Al is the slowing or stopping of root growth.

Extreme pH values decrease the availability of most nutrients.  Low pH reduces the availability of the macro- and secondary nutrients, while high pH reduces the availability of most micronutrients.  Microbial activity may also be reduced or changed.

Favorable pH ranges for common crops are listed in the table below.