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Chapter 18

Chapter 18- textbook

6 Pages
148 Views
Winter 2011

Department
Geography
Course Code
GGR100H1
Professor
Joseph Leydon
Chapter
18

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Chapter 18- The Geography of Soils 01:51
Soil Characteristics
Soil Profiles
A soil profile should be studied from the surface to the deepest extent of plant roots
or to where regolith or bedrock is encountered
Such a profile is a pedon, a hexagonal column measuring 1 to 10 m^2
A pedon is the basic sampling unit used in soil surveys
Many pedons together in one area make up a polypedon which has dsitinctibe
characteristics differentiating it from surrounding polypedons
A polypedon is an essential soil individual comprising an identifiable series of soils
in an area
Soil Horizones
Each distinct layer exposed in pedon is soil horizon
A horizon is roughly parallel to the pedons surface and has characteristics
distinctly different from horizons directly above or below
At the top of the soil profile is the O( organic) horizon named for its organic
composition derived from plant and animal litter that was deposited on the surface
and transformed into humus
Humus is not jus a single material; material usually dark in colour
At the bottom of the soil profile is the R(rock) horizon consisting of either
unconsolidated (loose) material or consolidated bedrock
The A, Ae, B, and C horizons mark differing minera strata btw O and R
The middle layers are composed of san, silt, clay, and other weathered by-products
The A horizon is mineral layer that forms at or near the surface
The removal of fine particles and minerals by water, leaving behind sand and silt is
termed eluviation this thus the e notation
The accumulation or enrichment of organic matter, oxides or clay dominates, or clay
dominates the B horizon
The depositions of these materials is known as illuviation
The combination of the A and E horizons and the B horizon is designated the solum,
considered the true definable soil of the pedon
Soil Properties
Soil Colour
Colour is important for its sometimes suggests composition and chemical makeup. If
you look at exposed soil colour ay be the most oblivious trait
However, colour can be deceptive: Soils of high humas content are often dark, yet
clays of warm- temperate and tropical regions with less than 3% organic content are
some of the worlds blackest soils
Soil Texture
Refers to the mixture of sizes of its particles and the proportion of different sizes
Individual mineral particles are soil separates, all particles smaller in diameter
part of soil , large particles not part of soil
www.notesolution.com
Loam which is a balanced mixture of sand, silt and clay that is beneficial to plant
growth
Soil texture is important in determining water-retention and water-transmission
traits
Soil Chemistry
Consequently, soil chemistry involves both air and water
The atmosphere within soil pores is mostly nitrogen, oxygen and carbon dioxide
Water present in soil pores is the soil solution. It is the medium for chemical
reactions in soil. This solution is critical to plants as their source of nutrients and it
is the foundation of soil fertility
Some ions in soil carry single charges, whereas others carry double or even triple
charges
Ions in soil are retained by soil collides. These tiny particles of clay and organic
material carry a negative electrical charge and consequently attract any positively
charged ions in the soil
Collides can exchange cations called cation-exchange capacity (CEC) which is the
measure of soil fertility
Therefore soil fertility is the ability of soil to sustain plants.Soil is fertile when it
contains organic substances and clay minerals that absorb water and adsorb certain
elements needed plants
Soil Formation Factors and Management
Natural Factors
These rocks supply the parent materials and their composition, texture and
chemical nature help determine the type of soil that forms
Climate types correlate closely with soil types worldwide. The moisture, evaporation
and temperature regimes of climates determine the chemical reactions organic
activity and eluviation rates of soils
Vegetation, animal and bacterial activity determine the organic content of soil,
along with all that is living in soil- algae, fungi, worms and insects. The chemical
makeup of the vegetation contributes to the acidity or alkalinity of the soil solution
Topography also affects soil formation. Slopes that are too steep cannot have full soil
development because gravity and erosional processes remove materials
All of the identified natural factors in soil development (parent material, climate,
biological activity, land forms and topography) require time to operate
Pedogenic Regimes
Soil- forming process are linked to climatic regions a connection that serves as the
basis for pedogenic regimes
Laterization is leaching process active in humid and warm climates
Stalinization concentrates salts in soils in climates with excessive potential
evaoptranspiration rates and is discussed with Solonetzic
www.notesolution.com

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Description
Chapter 18- The Geography of Soils 01:51 Soil Characteristics Soil Profiles A soil profile should be studied from the surface to the deepest extent of plant roots or to where regolith or bedrock is encountered Such a profile is a pedon, a hexagonal column measuring 1 to 10 m^2 A pedon is the basic sampling unit used in soil surveys Many pedons together in one area make up a polypedon which has dsitinctibe characteristics differentiating it from surrounding polypedons A polypedon is an essential soil individual comprising an identifiable series of soils in an area Soil Horizones Each distinct layer exposed in pedon is soil horizon A horizon is roughly parallel to the pedons surface and has characteristics distinctly different from horizons directly above or below At the top of the soil profile is the O( organic) horizon named for its organic composition derived from plant and animal litter that was deposited on the surface and transformed into humus Humus is not jus a single material; material usually dark in colour At the bottom of the soil profile is the R(rock) horizon consisting of either unconsolidated (loose) material or consolidated bedrock The A, Ae, B, and C horizons mark differing minera strata btw O and R The middle layers are composed of san, silt, clay, and other weathered by-products The A horizon is mineral layer that forms at or near the surface The removal of fine particles and minerals by water, leaving behind sand and silt is termed eluviation this thus the e notation The accumulation or enrichment of organic matter, oxides or clay dominates, or clay dominates the B horizon The depositions of these materials is known as illuviation The combination of the A and E horizons and the B horizon is designated the solum, considered the true definable soil of the pedon Soil Properties Soil Colour Colour is important for its sometimes suggests composition and chemical makeup. If you look at exposed soil colour ay be the most oblivious trait However, colour can be deceptive: Soils of high humas content are often dark, yet clays of warm- temperate and tropical regions with less than 3% organic content are some of the worlds blackest soils Soil Texture Refers to the mixture of sizes of its particles and the proportion of different sizes Individual mineral particles are soil separates, all particles smaller in diameter part of soil , large particles not part of soil www.notesolution.com
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