1

SOIL PROPERTIES

The various properties of soil include

1. Color

2. Texture

3. Humus

4. Soil structures

2

Color 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.

3

DIFFERENT SOIL COLORS

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.

4

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

5

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.

6

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.

7

Munsell Color ChartsHue = dominant spectral or “rainbow” color Red,

Yellow, Blue, Green

Number increases and the color is more brilliant as

grayness decreases

8

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

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.

10

Hums

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

11

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

Humus also controls the colour of soil higher the humus

content darker is the soil colour

12

13

TEXTURE

Refers to the size of

particles.

Three types are:

Sand (Large)

Silt (Medium)

Clay (Small)

14

SOIL STRUCTURE

The soil structures commonly

seen are-

1. Blocky

2. Platy

3. Massive

4. Prismatic

5. Granular

15

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.

16

2. PLATY

Large, thin

beds.

Plate-like &

arranged in

overlapping

horizontal

layers.

17

3. MASSIVE

Soil has no visible

structure.

Hard to break

apart & appears

in very large

clods.

18

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.

19

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.

20

21