Acidic soils occupy approximately 60% of the earth's land area. Soils become acidic when elements that are naturally acidic in reaction, like hydrogen ions, increase in concentration and lower the soil pH below 7. Acidic soils commonly form in humid, high rainfall areas due to leaching of basic cations like calcium and magnesium. They can also form from acidic parent materials like igneous rocks or due to excessive application of acid-forming fertilizers. Acidic soils have light texture, low organic matter and water holding capacity, and contain clay minerals like kaolinite. They negatively impact plant growth through both direct toxicity of hydrogen ions and indirect effects like aluminum toxicity and phosphate fixation. Approximately 49 million hectares of

1. *ACIDIC SOIL

2. *Introduction
*Soil acidity may be defined as the soil system’s
proton (H+ ions ) donating capacity during its
transition from a given state to a reference state.
*Soil having PH 5.5 are called acidic soil.
* Acid soil occupy approximately 60 % of the area of
earth .
*When the concentration of some elements which are
naturally acidic in reaction ,goes too high in soil ,soil
become acidic and their PH goes down below 7.

3. *Origin of Acidic soil
 CLIMATE: acidic soil are generally formed in humid
region and high rainfall areas.
* In these regions, evaporation of water from the soil
surface is less then precipitation .
* Excess amount of water moves downward in the soil
and leaching of nutrients like calcium and magnesium
takes place which results in formation of acid soil.

4. *Continue …
 PARENT MATERIAL : soil developing from
acidic rocks like igneous rocks results in
formation of acidic soil.
ACID FORMING FERTILIZERS: application of
acid forming fertilizers such as Ammonium
sulphate ,Urea, Ammonium nitrate etc. produce
soil acidity.

5. *Continue..
 ORGANIC MATTER: During organic matter
decomposition ,humus ,organic acids and different acid
salts may also be produced and also concentration of
Co2 increased .
* The increased concentration of Co2 , hydrolysis of acid
salts and various organic acids combinely increase the
total acidity of soil.

6. *Continue…
 HUMAN ACTIVITY : Excessive use of water or
keeping the field submerged for long time
accompanied by improper drainage may lead to
the development of acidic soil.

7. *Properties of Acidic Soil
PHYSICAL PROPERTIES:
* Light texture.
* High permeability
* Poor water holding capacity.
* Poor organic matter
* Mainly kaolinite and some time illite
clay minerals are present.

8. *Continue…
CHEMICAL PROPERTIES:
* More anion then cation.
* Availability of nutrients: Al,Fe,Mn,Cu,Co.
 BIOLOGICAL PROPERTIES:
* population of Fungi more then that of bacteria
* Rate of decomposition of biological materials
,mineralisation and nitrification etc. are reducesd
when acidity is increased.

9. *Effect of soil acidity on plants
DIRECT EFFECT:
* Toxic effect of H+ ions on root tissue.
* Phytoenzyme released by plant at root zone lose it
effectiveness if hydrogen concentration goes to high.
* Mineralization process becomes slow.
INDIRECT EFFECT:
* concentration of Al , Fe, Mg increased which cause
plant toxicity.

10. Iron toxicity in Rice
Mn Toxicity in cucurbits

11. *Continue…
* Deficiency of Calcium occurs.
*The phosphate ion reacts with Aluminum or iron and
insoluble phosphate of these element are formed
and become unavailable to the plant.
* Some essential micronutrient such as iron,
manganese, copper etc. are required by plants in
very low amount .they become highly soluble in
acidic soil and become toxic to plants.
*Some disease causing fungi flourished well in acidic
soil and cause root rot of tobacoo,blight of potato.

12. Aluminium toxicity in maize
Late blight (Fungi disease) in Potato

13. *Distribution of acidic soil
* Out of 146 million hectare of cultivable land in
India ,49 million hectare of land are acidic ,of
which 26 million hectare of land having soil PH
less then 5.6(PH < 5.6) and the rest 23 million
hectares of land having soil PH range 5.6 to 6.5.
*In India large area under acidic soil are Assam
,Manipur and Tripura .

14. Acidic soil found in India