Soil morphology

Soil morphology deals with the form, structure, and organization of the soil material, observed, described, and studied in the field, but investigation can be continued in the laboratory with optical and electron microscopes. This module explain the details of soil morphology.

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SOIL MORPHOLOGY
by
Prof. A. Balasubramanian
Centre for Advanced Studies in Earth Science
University of Mysore
India

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1. Definition:

Soil morphology deals with the form,
structure, and organization of the soil
material, observed, described, and studied in
the field, but investigation can be continued
in the laboratory with optical and electron
microscopes.

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Field observations with the unaided eye or
with a hand lens are considered
macromorphology, whereas observations
utilizing a microscope are considered
micromorphology.

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2. Soil morphology is the field observable
attributes of the soil within the various soil
horizons and the description of the kind and
arrangement of the horizons.
Soil morphology deals with the form and
arrangement of soil features.

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3. Soil Macromorphology :
Macromorphology is best evaluated from the
in situ examination of the soil profile.
A recently dug pit large enough for
observation of a pedon is desirable. Old
exposures such as road cuts and ditches are
acceptable only for preliminary examination
because morphological features often
become altered after prolonged exposure.

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The exposed profile should be probed by
hand, with the aid of a knife or small pick to
remove any alterations resulting from
digging equipment and to expose the natural
condition of the soil.
4. Micromorphology is a term used in
biology, mineralogy and soil science. The
fine-level structures or morphology of an
organism, mineral, or soil component visible
through microscopy.

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5. Soil Fabric, Structure and Assemblage -
Fabric is the mutual arrangement and
relationship between particles within the soil
as a whole and within the various features,
while structure is the type and degree of
aggregation. The totality of all features in a
specimen is called an ensemble or
assemblage. The main fabric relationships
seen in thin sections are in the fine earth.

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6. One of the most difficult tasks in
micromorphology is the recognition of
individual features. Clay particles are
themselves individuals; they cannot be
recognized with the optical microscope but
can only be identified with TEM or SEM
techniques.

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7. Recognition of patterns - most important
aspect of micromorphology is the recognition
of patterns, not only the pattern of single
individuals but also the relationships
between the individuals themselves. The
types of pattern range from the relatively
simple distribution of individual quartz
grains to the often complex distribution
pattern of clay coatings.

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Probably the most difficult patterns to
recognize are those of the anisotropism of
matrices. It is often difficult to describe
individuals and patterns. In many cases a
true representation can only be achieved
with good photographs and diagrams.

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8. Quantification of features: core
samples are required to characterize
quantitatively coatings, matrices, pores and
concretions in horizons with translocated
clay.
9. Interpretation of features and patterns:
This is based on a combination of experience,
intuition and guess-work.

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10. Properties of features and minerals:
The main properties are: color, prominence,
size, shape frequency, roundness, sphericity,
surface characteristics, boundaries,
distribution pattern, relationships between
features and orientation

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11. Field morphology : in situ examination
of a soil profile. Study of soil morphological
features in the field by thorough observation,
description and interpretation. with the aid
of a hand lens. tests are in the field to record
salient chemical properties (e.g., pH,
presence of carbonates). Evaluation of
chemical, biological and physical attributes.

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12. The delineation of horizons is
necessarily a somewhat subjective processes
because changes in soil attributes are often
gradational rather than abrupt.
Standard profile descriptions:
Depth intervals of horizons or layers
(measured from the top of the mineral
horizon)
Horizon boundary characteristics
Color

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Texture,
Structure,
pores,
Consistence,
Distribution of Roots,
pH and
effervescence.
Special features such as coatings, nodules,
and concretions.

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13. Soil Site Characteristics :
Soil site characteristics are as important as
the profile description to a comprehensive
soil description. Whereas, the profile
description details the internal organization
of the soil, a site description details the
landscape of the soil. Soil distribution is
substantially determined by landscape
features.

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Some of the site characteristics important to
a soil description are:
1. Relief/
2. Microrelief /
3. Elevation ./
4. Slope (gradient, length, aspect, surface,
configuration)/
5. Vegetation /6. Parent material
7. Erosion /8. Depth .

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14. Relief=
relief refers to the differences in elevations of
landscape features.
It is expressed in units appropriate to the
scale of the landscape.

15. Microrelief : refers to the differences in
elevation of landscape features over
distances of centimeters to meters.

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Microrelief would take into account small
knolls and swales, coppice dunes, and gilgai.

16. Elevation :
The soil elevation is the vertical distance of
the soil above mean sea level. This can be
determined by locating the soil site on a
topographic map.

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17. Soil slope :
Soil slope = distinct properties: gradient,
length, aspect, and surface configuration.
Slope influences many aspects of soil
development, such as water movement,
runoff, erosion, and other factors. It is
expressed as an angle between 0 and 360
degrees .

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18. Surface configuration describes the
shape of the local landscape.
An alluvial fan and the shoulder of a ridge
both have a convex slope, in which the
gradient increases downslope.
Foot slopes have a concave slope in which
the gradient decreases downslope.

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19. Vegetation :
An estimate should be made of the kinds and
amounts of natural vegetation present.
Notes of this kind can help to clarify or even
discover plant-soil relationships.
Recognition of plant communities and
knowledge of soil-plant relationships can aid
in the identification of soil boundaries.

20. Parent Material :

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Parent material is the material from which
the soil has formed. These deposits range in
character from organic peat to
unconsolidated rock. Parent material can
either form in place or be transported from
elsewhere.
Residual, or parent materials formed in
place, include weathered igneous,
sedimentary, and metamorphic rocks.

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Transported parent materials are moved by
wind, water, ice, or gravity. Wind
transported materials include ash, loess, and
sand. Water transported materials include
alluvial, lacustrine, marine, and beach
deposits. Ice transported materials= glacial
drift.

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21. Soil Erosion :
The degree to which accelerated erosion, or
that induced by man, has affected soil
formation and suitability for management is
evaluated in a site description. The effect of
erosion can then be determined by a
comparison. Soils are divided into erosion
classes based on the amount of material lost
from the soil surface.

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22. Soil Depth:

Soil depth is determined by the total
thickness of soil horizons that are significant
to soil use and management.

It is normally the depth to which plant roots
develop.

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Soil depth is described as either deep,
moderate, shallow, or very shallow to a
restrictive layer.
Restrictive layers include cemented horizons,
clay pans, bedrock, and sometimes abrupt
textural changes.