2. Soil mapping units
•Mapping unit may be defined as the classification of
areas having similar soil components.
•It differ from other mapping unit in some of the soil
characteristics depending upon the purpose, the
following mapping units are being used in different
kinds of soil survey.
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3. A soil map delineates the areas occupied different kinds
of soils
Each has unique set of inter- related properties,
materials its environment and history.
A map unit is a collection of soil components or
miscellaneous areas or both
Each map units differs in some respect from all others in
a survey area and is uniquely identified on a soil map.
Map units consists of one or more components
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4. An individual component of a map unit represents the
collection of polypedons or parts of polypedons that are
members of the taxon or a kind of miscellaneous area
(inclusion)
Soil boundaries are shown on maps by lines.
Area enclosed by a boundary is called a soil delineation
Several map units on a map unit symbols, colors and
names is called as map legend
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5. Soil series
•A soil series is a taxonomic unit represents a group of
soils having horizons similar in characteristics and
arrangement in a soil profile developed from a particular
type of parent material but they may differ in the surface
texture.
•It is given a geographical name either of locality where it
is well developed or where it was recognized first.
•For establishing a soil series we should require a
minimum area of 2000 acres.
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7. The characters considered for characterization of a
soil series are
Kind and arrangement of
soil horizon
• Texture
• Thickness of individual
horizon
• Consistency
• Solum depth
• Concretions
• Soil color
• Soil structure
• Mottling's
• Soil pores
• Presence of clay films/
Slickensides
• Development of surface
cracks
• Root distribution
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8. •By using profile characteristics we differentiate the
soils in the field.
•The physical and chemical characteristics are not
taken for mapping.
•The environmental characters like slope, topography,
stoniness, rockiness, soil erosion and the surface
layers are taken in to account for characterizing the
soil.
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9. Soil type and Soil phase
Soil type
It refers to the surface texture of soil series. It is
denoted by the name of the soil series followed by the
texture of the surface layer. eg: Plm - sandy loam
Soil phase
This is a mapping unit classified based on the
environmental characters of the soil series namely
slope, erosion, stoniness etc.
Type and phase mapping units are used in detailed
soil survey.
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10. Inclusion andVariants
Inclusion
These are the soil not denoted in soil map. They are
so small to be delineated. Normally soils which occupy
less than 20 per cent of the mapping area belongs to this
type.
Variants or polypedons
These are soils of a established series differing in
some properties of the series. They are indicated as
variant of the series in reconnaissance soil series. These
variants will be proposed as a new series during detailed
soil survey.
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11. Mapping Symbol
•Maps use symbols to represent features on the ground.
These features include roads, tracks, rivers, lakes,
vegetation, fences, buildings, powerlines, administrative
boundaries and the like.
•Given the size of a map, it is not possible to show all
features that occur on the ground.
•Large scale maps show more details and a larger
number of features.
•Colour plays an important part in symbols for example,
blue for water features and green for vegetation.
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12. Map scale
•A map represents a given area on the ground. A map
scale refers to the relationship (or ratio) between distance
on a map and the corresponding distance on the ground.
•Map scales can be shown using a scale bar.
•Based on the scale of mapping, the map is called as
Large scale maps - 1: 5000 and less
Medium scale maps - 1:25,000 to 1:40,000
Small scale maps - 1:50,000 to 1: 2, 50,000
Very small maps - 1: million and above
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13. Taxonomic unitsVersus Mapping units
•Taxonomic units define specific range of soil properties
in relationship to the total range of properties measured
in the soil.
•The map units and their individual delineations define
areas on a landscape.
•Every mapping unit has more than one taxonomic unit
(soil series or soil phase).
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14. Kind of mapping units
Mapping units have been distinguished based on
the amount of inclusion or impurity they contain. Five
kind of mapping units have thus been distinguished and
these are,
Consociation
Association
Complex
Undifferentiated
Miscellaneous/unvisited.
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15. Consociation
•A consociation is a mapping unit with very little inclusion
or impurity. It is assumed to contain the profile class
after which it is named but in practice the purity of such
class may range from 70% to 85%.
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16. Association
•It is a mapping unit consisting of two or three soil series
occur in a repeated geographical pattern. The
boundaries of soil series can not be demarcated
separately due to map scale limitation.
•eg: Palathurai - Pichanur soil series occur in association.
This major soil series should be written first followed by
the minor. Here also three letter symbol is used.
•Pth - Pch (Palathurai - Pichanur)
•Plm - Pth - Pch (Pilamedu - Palathurai - Pichanur)
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17. Soil Complex
•It is a mapping unit consisting of more than three
series occurring together in a repeated geographical
pattern.
•Boundaries can not be demarcated separately.
•It is a mapping unit in hilly terrains. It is indicated by
Roman letters.
•The mapping units namely soil series, association and
soil complex are used in the Reconnaissance soil
survey.
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18. Undifferentiated
•This is a mapping unit consisting of a number of
taxonomic units that are merged so that separation
into different units are impossible at any reasonable
mapping scale
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19. Miscellanceous land types
•The areas which have little or no soil to support any
vegetation are named as miscellaneous land types.
•These areas could be used only after proper
reclamation.
•Mostly they are non soil however, they are indicated
along with soil series, associations and complexes.
i. Water bodies iv. Rubble lands
ii. Salt pans v. Rock out crops
iii. Sand dunes vi. Ravines …. etc.
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