This Power Point Presentation intends to explore the different horizons of soil along with the factors expedite the soil formation from parent rock.

1. PLANT ECOLOGY
Soil profile; Role of climate in soil
development.
By
N. Sannigrahi, Associate Professor
Department of Botany
Nistarini College, Purulia (W.B) India

2. SOIL PROFILE
 Due to interaction of various factors, the Pedogenesis process
develops a variety of soil types catalyzed by the different
climatic, topographic and biological factors. Different type of
soil may be defined by the nature of the mineral matrix, the
vertical distribution of organic matter and the movement and
redeposit ion of various inorganic components. Soils are
described and identified by reference to their profiles. Soil
profile is “ the sequence and nature of horizons (layers)
superimposed one above the other and exposed in a pit-section
dug through the soil mantle". The smallest three dimensional
volume of a soil needed to give full representation of horizontal
variability of soil is termed as pedon. A soil horizon is defined
as “ a layer which is approximately parallel to the soil surface
and that has properities produced by soil forming

3. SOIL PROFILE
 Processes but that are unlike those of adjoining layers". The
soil consists of many distinct layers which differ in structure ,
thickness, consistency, texture, porosity, color, chemical
composition etc. The various layers are termed as soil profile.
In other words, the sequence of succession of horizons from
the surface downwards is called the soil profile.
 The soil profile is generally consists of the following layers as
stated below:
 The ‘O’ horizon-consists of O1 and O2
 The ‘A’ horizon-consists of A1 & A2
 The ‘B’ horizon-
 The ‘C’ horizon-
 The ‘R’ horizon

4. SOIL HORIZONS

5. THE ‘O’-HORIZON
 The organic horizon forming above the surface of the mineral
matrix mainly composed of fresh or partially decomposed
organic matter. Mostly found to develop in the forest and
completely absent in grassland. It is divided into the following
two sub-layers-
 O1 Horizon-Uppermost layer consisting of fallen dead organic
matter as dead leaves, branches, flowers, fruits and dead parts
of different animals without any broken evidences.
 O2 Horizon-Just below the decomposition of the former layer
having organic matter found under different stages of
decomposition and microorganisms like fungi, bacteria and
Actinomycetes. Upper layers consists of detritus in initial
stages whereas the lower layers contain fairly decomposed
matter , the duff.

6. THE ‘A’-HORIZON
 Formed at or adjacent to the surface, these are rich in organic
matter and show downward loss of soluble salts , clay , iron or
aluminium.This is also known as zone of eluviations-
downward loss or leaching. It is mainly divided into the two
sub-layers-
 A1 Region-The amorphous, dark, rich in organic matter with
mineral matter admixture. The region having a mixture of
finely divided organic matter and mineral matter called humic
or mineralized region.
 A2 Region- The region is light color with mineral particles of
large size as sand or more with little amount of organic matter.
Mostly found to grow in the heavy rainfall regions, the mineral
elements and the organic matter rapidly lost downward. Called
podosolic or eluvial zone or zone of leaching.

7. THE ‘B’HORIZON
 These are basically mineral horizons forming below the surface
having the following features-enrichment with in washed clay (
lessivation), iron, aluminum, manganese or organic matter,
(ii)residual enrichment with sesquioxides or silicate clays
which has occurred other than by the removal of carbonates or
the silicate clays or readily soluble salts, iii) sesquioxide
coatings of mineral grains sufficient to give a more intense
color than horizons above or below, iv) alteration of the
original rock material to give silicate clays or oxides in
conditions where the first three are not applied. This can be
divided into different sub-layers .The B horizon is dark colored
and coarse textured due to the presence of silica-rich clay
organic compounds, hydrated oxides of aluminum, iron etc.
Since, the chemical leached from A2 region, become collected
in this horizon.A1,A2 and B collectively called solum.

8. THE ‘C’ HORIZON & ‘R’ HORIZON
 ‘C’-Horizon : These are mineral horizons below B but
excluding true bedrock and without any characteristics of A’ or
‘B’ horizons. It completely consists of weathered, large masses
of rocks.
 ‘R’ Horizon: This is parent, unweathered bed rock, upon which
there is collected water. It is lowermost stratum or layer of the
soil.
 Soil profiles vary from place to place. The nature of the soil
profile depends more on the climate and vegetation than on any
parent rock from which the soil is originally formed. Usually,
the topsoil is thicker in forest than in grassy areas. Places
devoid of vegetation or with poor plant growth may have no
topsoil , and the subsoil then extends to the surface.

9. ROLE OF CLIMATE IN SOIL DEVELOPMENT
 The whole sequence of soil formation- weathering and
pedogenesis comprising of many factors. The nature and type
of soil, forming at a particular place is largely governed by the
nature of the parent material and its interaction with climate,
topography , organisms etc. The different factors in general and
climate in particular play a very important role in this regard.
Any soil property(s) is a collective function or the effects of all
pedogenic factors (Jenny, 1991):
 S = f (cl, o, r, p. t.) where f = function dependent upon a set of
conditions.
 The climate plays a very crucial role in the process of soil
formation whether it is pedogenesis or weathering along withy
their journey of soil formation.

10. ROLE OF CLIMATE IN SOIL
DEVELOPMENT
 RAINFALL: Rainfall determines the direction of solute
translocation according to precipitation/ evaporation (P/E)
ratio. In combination of other factors, rainfall also determines
depth to water table, which would affect the level of capillary
water and aeration during the weathering and pedogenesis.
 TEMPERATURE: Through its interaction with precipitation, it
governs P/E ratio. Through its influence on physico-chemical
processes, it controls the rate of organic turnover in soil. Also,
it affects growth rate of vegetation and other organisms.
Temperature and precipitation influence how fast parent
materials weather and, thus, soil properties such as mineral
composition and organic matter content.
 Temperature directly influences the speed of chemical
reactions. The warmer the temperature, the faster reactions
occur. Temperature fluctuations increase physical weathering
of rocks.

11. ROLE OF CLIMATE IN SOIL DEVELOPMENT
 PRECIPITATION governs water movement in the soil. The amount
of water the soil receives and the amount of evapo-transpiration that
occurs influence water movement. Normal annual precipitation in
 Minnesota is the least in the northwest corner at 16 inches, and
increases as you go toward the southeast corner, where 34 inches is
the normal annual precipitation
 HUMIDITY: Their interaction influence the rainfall and the amount
of water movement.
 MOISTURE INDEX
 A leaching index or moisture index is calculated by subtracting
evapo-transpiration from precipitation. This index is an indicator of
average soil moisture conditions.
 The greater the index, the more soil moisture is present. Higher soil
moisture increases chemical weathering and moves minerals, such as
bases, deeper into the soil profile. This affects management practices
such as drainage and inputs of mobile nutrient

12. THANKS FOR YOUE PLEASURE
 ACKNOWLEDGEMENT
 1.Google for images
 2.Different WebPages for content
 3.Ecology & environment-P.D.Sharma
 4.Ecology & Environmental Biology- T.K.saha
 5. A text book of Ecology- S.Chand & company.
 Disclaimer: This PPT has made as a free learning
resources for academicians, teachers, students and others
without any financial interest.