Soil Acidity and Alkalinity : Biogeography

 

Soil Acidity and Alkalinity

• Soil pH is a measure of the concentration of hydrogen ions in the soil solution. The lower the pH of soil, the greater the acidity.
• pH should be maintained at above 5.5.  
• pH between 6.5 and 7.5 is considered to be neutral soils.

Soil acidity

• 5-6 pH is common in humid soils like Laterite soils. 
• Strongly acidic soils with pH 4-5 are found in some podzols due to high organic action and formation of humic acid.

Impact :

• Extremely acidic soils are toxic due to high aluminium concentration. When soil pH drops, aluminium becomes soluble. A small drop in pH can result in a large increase in soluble aluminium. In this form, aluminium retards root growth, restricting access to water and nutrients. 
  
• Mild acidic soils can be treated by Lime and turned into cultivable soils. 

Soil alkalinity.

• Sub humid and semi arid regions have alkalinity of range 8 to10. These soils are rich in minerals and hence fertile like Chernozem, Chestnut and Prairies soils. 
• Extreme alkalinity of range 10-11 pH, where salt concentration is high mostly due to unscientific agricultural practices by human beings. 

 

Impact 

• Formation of salt pans, Iron pans restricting percolation of water and creating waterlogged conditions.
• Higher alkalinity reduces available free Iron for the plants to absorb, turning the leaves to pale colour.
• High alkalinity can be toxic for plant growth. 

A well maintained soil pH will maintain the value of the soil resource, maximize crop and pasture choice and avoid production losses due to low pH.