Factors affecting soil pH

1. Factors Affecting Soil pH

2. Parent material of the soil
 Soils formed from basic rocks like limestone have higher soil pH, meaning they
are alkaline.
 Soils formed from sandstone have low pH value, meaning they are more acidic.

3. Leaching
 During heavy rainfall the alkaline nutrients such as calcium (Ca2+) and magnesium
(Mg2+) are washed deep down the soil horizon.
 Such leached ions are replaced by hydrogen ions. This reduces soil pH, making it
more acidic.

4. Use of acid forming fertilizers
 Heavy use of fertilizers such as ammonium sulphate makes the soil acidic.
 The sulphate ions from the fertilizer combine with hydrogen ions from water
resulting in formations of sulphuric acid. This reduces soil pH.

5. Activities of living organisms in the soil
 Decomposition of organic matter by living organisms releases of hydrogen ions.
 This increases the concentration of hydrogen ions in the soil. The result is that
soil pH is reduced, making the soil acidic.

6. Nutrient uptake by plants
 Plants absorb various cations (positive ions) from the soil as they grow.
 Once crops are harvested cations are reduced from the soil mainly when crop
remains are not incorporated back into the soil.
 The lost cations are then replaced with hydrogen ions. This reduces soil pH,
meaning the soil become acidic.
 Hydrogen ions replace the lost cations, reducing soil pH.