Upload
avnee-kashyap
View
526
Download
3
Tags:
Embed Size (px)
Citation preview
SOIL PROPERTIES AND CLASSIFICATION
SOIL PROPERTIES The various properties of soil include-
1. Color
2. Texture
3. Humus
4. Soil structures
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.
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.
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
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.
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
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
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.
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
•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.
TEXTURE Refers to the size of particles.
Three types are….Sand (Large)Silt (Medium)Clay (Small)
TEXTURE = % of sand , silt and clay.
SOIL STRUCTURE The soil structures commonly
seen are-
1. Blocky
2. Platy
3. Massive
4. Prismatic
5. Granular
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.
2. PLATY
Large, thin beds.
Plate-like & arranged in overlapping horizontal layers.
3. MASSIVE
Soil has no visible structure.
Hard to break apart & appears in very large clods.
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.
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.
SOIL CLASSIFICATION
Soil can be classified according to the grain size as-
1. Fine grained- Clay
2. Medium grained- Silt
3. Coarse grained- Sand
CLAY < 0.002 mm Flat plates or tiny
flakes Small clay particles
are colloids If suspended in
water will not settle
Wet clay is very sticky and is plastic or it can be molded readily into a shape or rod.
Easily formed into long ribbons
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
SILT < 0.05 mm to >
0.002 mm
Not visible without microscope
Quartz often dominant mineral in silt since other minerals have weathered away.
Does not feel gritty
Floury feel –smooth like silly putty
Smaller particles – retains more water for plants and have slower drainage than sand.
Easily washed away by flowing water – highly erosive.
Holds more plant nutrients than sand.
SAND Feels gritty Considered
non-cohesive – does not stick together in a mass unless it is very wet.
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
On the basis of texture soil can be classified as :-1. Sandy soil2. Loamy soil3. Clayey soil
Sandy Soils
Coarse textureSandsLoamy sands
Loamy Soils- Coarse
Medium textureVery fine
sandy loam
LoamSilt loamSilt
Loamy Soils - Fine
Moderately fine textureSandy
clay loamClay loamSilty
clay loam
Clayey Soils
Fine textureSilty clayClaySandy clay
tHANK YOU