This document discusses soil properties and classification. It describes several key soil properties including color, texture, humus, and structure. Soil color is influenced by mineral content, organic matter, iron, and moisture levels. Texture refers to particle size and is classified as sand, silt, or clay. Humus is decayed organic matter that provides nutrients and improves soil structure. Common soil structures include blocky, platy, massive, prismatic, and granular formations. Soils can be classified based on texture as sandy, loamy, or clayey soils.

1. SOIL PROPERTIES
AND
CLASSIFICATION

2. SOIL PROPERTIES
 The various properties of soil include-
1. Color
2. Texture
3. Humus
4. Soil structures

3. COLOUR
 Colour is the foremost physical
property that can be seen with naked
eye and is useful in interpretation of
valuable insight into the soil
environment, thus it can be very
important in assessment and
classification of soil.

4. DIFFERENT SOIL
COLOURS
 The most influential colours in a well
drained soil are white, red, brown
and black.
 White indicates the predominance of
silica (quartz), or the presence of
salts.
 Red indicates the accumulation of
iron oxides.
 Brown and black indicate the level
and type of organic matter. A colour
triangle can be used to show the
names and relationships between
the influential colours.

5. FACTORS DETERMINING
SOIL
COLOUR
 Four main factors influence the colour of
a soil:
1. Mineral matter derived from the
constituents of the parent material
2. Organic matter
3. The nature and abundance of iron
4. Moisture content

6. INTERPRETATION USING
SOIL COLOUR
 If we understand what determines soil
colour, then we can use colour to make
some inferences
about, history, chemistry and hydrology.
 For example, an obvious change in
colour between horizons is a real
indication of changes in soil properties
which are the result of biological
activity, water movement and
weathering.

7. DETERMINING SOIL
COLOUR
 Soil colour should be determined on moist surfaces
of freshly broken (not sliced) soil samples.
 Like any other soil property, colour must always be
observed throughout soil profile, paying special
attention to the differences between soil horizons.
Colour characteristics such as mottle
size, percentage and contrast should be observed
and recorded.
 A system that uses specially printed colour charts
(Munsell Soil Colour Charts) gives an international
standard. It divides colour into
wavelength, lightness, and colour saturation.
 Where a Munsell Chart is not available, simple
names as listed in the triangle can be used.

8. Munsell Color Charts
Hue = dominant spectral or “rainbow” color
Red, Yellow, Blue, Green
 Number increases and the color is more
brilliant as grayness decreases
8

9. Color Determination in the field
 ALWAYS USE MOIST SOIL
 Munsell’s color charts values:-
1. Absolute black = 0
2. Absolute white = 10
3. Light soils hue value = 7 or more
4. Medium soils hue value = 5 – 6
5. Dark soils hue value = 4 or less
9

10. MOTTLES
 Spots of different colors in the soil
 Generally indicate that the soil has
periods of inadequate aeration each
year
 Usually rust colored
 Bluish, grayish, & greenish subsoils –
with or w/o mottles = indicate longer
periods each year of waterlogged
conditions & inadequate aeration.

11. HUMUS
 The term was coined in1790–1800; (< Latin:
earth, ground)
 Dark brown or black organic substance
made up of decayed plant or animal
organic matter, that provides nutrients
for plants and increases ability of soil to
retain water

12. •In soil science, humus refers to any organic matter that has
reached a point of stability, where it will break down no
further and might, if conditions do not change, remain as it is
for centuries. Humus significantly improves the structure of
soil and contributes to moisture and nutrient retention.
•In agriculture, humus is sometimes also used to describe
mature compost, or natural compost extracted from a forest
or other spontaneous source for use to amend soil. It is also
used to describe a topsoil horizon that contains organic
matter

13. Humus also controls
the colour of soil
higher the humus
content darker is the
soil colour.

15. TEXTURE
 Refers to the size of particles.
 Three types are….
 Sand (Large)
 Silt (Medium)
 Clay (Small)
 TEXTURE = % of sand , silt and clay.

16. SOIL STRUCTURE
 The soil structures commonly
seen are-
1. Blocky
2. Platy
3. Massive
4. Prismatic
5. Granular

17. 1. BLOCKY
 Particles cling
together in angular
aggregates.
 Typical of soils with
high clay content.
 Typical of B
horizons.
 beds are large
about 5 to 50
millimeters.

18. 2. PLATY
 Large, thin beds.
 Plate-like &
arranged in
overlapping
horizontal
layers.

19. 3. MASSIVE
 Soil has no visible
structure.
 Hard to break
apart & appears in
very large clods.

20. 4. PRISMATIC
 Prismatic structure are
bounded by flat to
rounded vertical
faces. Units are longer
vertically and top of
the prisms are
normally flat.
 It is commonly found
in B horizons.

21. 5. GRANULAR
 Is the best for most
plants.
 Particles cling
together to form
rounded aggregates.
 It is commonly found
in A horizons.
 Beds are small
usually between 1 to
10 millimeters.

22. SOIL
CLASSIFICATION
 Soil can be classified
according to the grain size as-
1. Fine grained- Clay
2. Medium grained- Silt
3. Coarse grained- Sand

23. CLAY
 < 0.002 mm
 Flat plates or tiny
flakes
 Small clay particles
are colloids
 If suspended in
water will not settle

24.  Wet clay is
very sticky and
is plastic or it
can be molded
readily into a
shape or rod.
 Easily formed
into long
ribbons

25.  Pores spaces are very
small and convoluted
 Movement of water
and air very slow
 Water holding capacity
 Tremendous capacity
to adsorb water- not
all available for plants.
 Chemical adsorption is
large

26. SILT
 < 0.05 mm to >
0.002 mm
 Not visible without
microscope
 Quartz often
dominant mineral in
silt since other
minerals have
weathered away.

27. Does not
feel gritty
Floury feel
–smooth
like silly
putty

28.  Smaller particles –
retains more water
for plants and have
slower drainage
than sand.
 Easilywashed
away by flowing
water – highly
erosive.
 Holds more plant
nutrients than
sand.

29. SAND
 Feels gritty
 Considered
non-cohesive
– does not
stick together
in a mass
unless it is
very wet.

30.  Sand has less
nutrients for plants
than smaller particles
 Voids between sand
particles promote free
drainage and entry of
air
 Holds little water and
prone to drought

31. On the basis of
texture soil can be
classified as :-
1. Sandy soil
2. Loamy soil
3. Clayey soil

32. Sandy Soils
 Coarse
texture
 Sands
 Loamy
sands

33. Loamy Soils- Coarse
 Medium
texture
 Very fine
sandy loam
 Loam
 Silt loam
 Silt

34. Loamy Soils - Fine
 Moderatel
y
fine
texture
 Sandy
clay loam
 Clay loam
 Silty
clay loam

35. Clayey Soils
 Fine texture
 Silty clay
 Clay
 Sandy clay

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