New Update Causes of soil acidity

B.Sc.Ag. (Hons) Part-III    

Causes of soil acidity. https://cststudy.blogspot.com

Causes of soil acidity:

1. Leaching of basic cation by heavy rainfall: CO2 dissolve in water to produce carbonic acid (H2CO3). These H2CO3 removes the basic cations (i.e. Mg+, Na+, Ca2+, K+) from alkaline soil and form bi-carbonate which are soluble in water. These bi-carbonate are leach down due to heavy rainfall and causes soil acidity.
CO2 + H2O ---->H2CO3

H2CO3 ----->H+ + HCO3

2. Acidic parent material: Some soil have developed from acidic parent material, so the soil are acidic soil. E.g. Acid rock (granite) weathering    Acid soil.

3. Increase acid cations (Al3+, Fe3+, Mn4+): These are ions are hydrolysis produce H+ ion in soil and thus causes soil acidity.

Al3++ H2O —> Al(OH)2++ H+ (for strong acid)
Similar reaction will be occur in case of Fe3+ and Mn4+. Al3+ and H+ are two acidic cations which arc mainly responsible for soil acidic.

4. Alumino-silicate minerals: At low P" values most of the Aluminium is present as the hydrate. Aluminium ions (Al3+) which undergoes hydrolysis and release hydrogen Oil ions in the soil solution that develop soil acidity.
Al3++ H2O —> Al(OH)2++ H+

5. Application of manures and fertilizers: Manures- by decomposition of different types of organic matter in soil produce different types of organic acid. e.g. pulmic acid. These organic acid produce H+ which can create soil acidity.

Cowdung----> Protein ----> R-NH2  --->      NH4+ oxygen ---->NO2-  oxygen  -----> NO3- + acidic soil.

Ammonium sulphate decrease PH more than Urea. So, it is-usually apply in tea garden.

Urea CO(NH2)2  ----> NH4+ oxygen ---->  NO2-+ H+   oxygen --->   NO3-  (Soil acidic)

6. Carbon-dioxide (CO2): Root activity and metabolism may serve as source as CO, which dissolved in soil water and produce Carbonic acid (H2CO3). As a result, soil acidity occurs.
CO2+ H2O -----> H2CO3

7. Acid rain: In industrial area SO2 and NH3 etc. are present in high amount. These mix with rain water and come down to the earth and causes soil acidity.
NH3 oxygen      NO3- water     HNO3   rain        Acidic soil.
SO2   water      H2SO4   rain      Acidic soil

8. Acid sulphate soil: Oxidized form of SO42- and Fe3+ converted into reduced form when the land receive tidal flood. These reduced form react together to form FeS2. This FeS2 is Oxidized to Fe2(SO4)3. As a result, decreases and acidity of soil occur.

  -->Fe3+ ---          Fe2+, SO42-   -----> H2S

H2S + Fe2+ ----> FeS2 oxygen ----->   Fe2(SO4)3   (acidic sulphate)


9. Nutrient Uptake: In rhizosphore cation and anion ratio 1:1 always same. If H+ uptake increases then soil acidity increases i.e. soil PH decreases. When OH- Uptake increases then soil alkalinity increases i.e. PH increases. 



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