What is soil Ph

What is soil Ph

Soil pH is the degree of acidity or alkalinity of the soil.

PH stands for potential of Hydrogen i.e. the concentration of hydrogen ions in the soil. It is calculated using the formula,

 pH = – log H+      OR    pH = log [1/H+}

The degree of acidity depends on the concentration of hydrogen ions,

When the soil is acidic; hydrogen ion concentration exceeds hydroxyl ion concentration.

When the soil is neutral, hydrogen ion concentration equals hydroxyl ion concentration.

When the soil is alkaline or basic, hydroxyl ion concentration is greater than hydrogen ion concentration.

The pH scale

pH ranges from 1 to 14

pH 7 is neutral

Above pH 7, the soil is alkaline or basic.

 Below 7, the soil is acidic.

Causes of soil acidity

Presence of acidic soluble salts which may arise from fertilizers, weathering of minerals etc.

Leaching of bases which are later replaced by hydrogen ions.

Presence of acidic organic matter.

Water logging

Acidification due to rain water

Biological activities in the soil

Artificial fertilizers e.g sulphate of ammonia

Uptake of bases by plants

The soil may have been formed from acidic parent material e.g granite

Causes of soil alkalinity

Weathering of limestone.

Addition of bases e.g lime.


Drought conditions

Ground water