Soil formation or pedogenesis is the combined effect of human impact on the environment, physical, chemical and biological processes working on soil parent material.

1. What is Soil Formation?
 Soil formation or pedogenesis, is the combined effect of human
impact on environment, physical, chemical and biological
processes working on soil parent material.
 Climate regulates soil formation. Soils are more developed in
areas with higher rainfall and more warmth.
 The rate of chemical weathering increases by 2-3 times when
the temperature increases by 10 degree Celsius.

2. Soil Forming Processes
Addition
Loss
Translocation
Transformation

3. Processes of Horizon Formation in the Soil Profile
 Addition
 Water from rainfall.
 O2 & CO2 from the atmosphere.
 OM from decomposition of plants & animals residues.
 Eroded materials from sediments
 Nutrients or ions from rain water, atmosphere, etc.
 Energy from sunlight

4.  Losses
 Water through evapotranspiration.
 Nitrogen by denitrification & volatilization.
 O2 & CO2 through oxidation of OM.
 Soil by erosion
 Water & nutrients by leaching.
 Energy by radiation.

5.  Translocation (from one location to another)
 Salts that are dissolved in water.
 Nutrients that cycle in plants.
 Soil by animals, e.g.. Earthworms

6. Eluviation
 It is the mobilization and translocation of certain constituent’s viz. Clay,
Fe2O3, Al2O3, SiO2, humus, CaCO3, other salts etc. from one point of soil
body to another.
 It is the process of removal of constituents in suspension or solution by
the percolating water from the upper to lower layers. The horizon formed
by the process of eluviation is termed as eluvial horizon (A2 or E horizon).

8.  Transformation
 Physical weathering that change size of rocks.
 Chemical weathering that change or produce various salts or
nutrients.
 Formation of humus by decomposition of OM.
 Reactions of clay with OM.

9. 1. Melanization
2. Gleization
3. Calcification
4. Podzolization
5. Laterization

10. Melanization
 Melanization is the
development of dark,
humus-rich coatings on
ped faces and mineral
grains, rendering the
horizon a dark brown
or black.
 This process is very
common in the regions
of low humidity where
humus is formed from
the organic matter.

11.  Due to melanization the
black humus along with
water is mixed in the A-
horizon which becomes
dark coloured.
 The degree to which a
soil becomes melanized
is a function of the rate
and duration of humus
production.

12. Gleization
 The term ‘glei’ is of Russian origin which
means blue, grey or green clay.
 Gleization is a process of soil formation
resulting in the development of a glei (or
gley horizon) in the lower part of the soil
profile above the parent material due to
poor drainage condition (lack of oxygen)
and where waterlogged conditions prevail.

14.  The process is not particularly dependent on
climate (high rainfall as in humid regions) but
often on drainage conditions.
 Under reducing conditions,
 Due to ferrous compounds, the soil colour
becomes blue-grey or grey, and
 The rate of decomposition of organic matter is
very low.
These together result into the accumulation of a
sticky, compact layer of blue-grey or grey colour
at the bottom of B- horizon. This process is
called ‘gleization’ and the soil is called ‘glays’.

15. Calcification
 It is the process of precipitation and accumulation of
calcium carbonate (CaCO3) at the base of B- horizon.
 It is typical of grassland and occurs in areas of low
precipitation.
 The accumulation of CaCO3 may result in the
development of a calcic horizon.
 Calcium is readily soluble in acid soil water or when CO2
concentration is high in root zone.

17. Podzolization
 It is a process of soil formation resulting in the
formation of Podzols and Podzolic soils which are
highly acidic and infertile.
 It is the negative of calcification.
 Conifers produce leaf litter contains:-
 high lignin and low nutrient (Ca) contents,
 rich in phenolic compounds which inhibit microbial
activities,
 layer is acidic in nature.

19. Laterization
 It refers specifically to a particular cemented horizon
in certain soils which when dried, become very hard,
like a brick. Such soils (in tropics) when massively
impregnated with aluminium and iron sesquioxides
to extent of 70 to 80% of the total mass, are called
laterites. The soil forming process is called
Laterization.
 Under high temperature regimes and high rainfall in
the tropics, the silicate minerals are very unstable.
 These sesquioxides of the parent minerals are
resistant to decomposition.
 It leaves a residue of primary laterite.

21. Thank You 