Soil Science

1. SoilProfile
Soil horizons
Soil horizons are the parallel layers you notice in a cross-sectionof your
ground. Horizons are identified beginning at surface level with the O horizon, and
moving down through A, E, B and C horizons until finally arriving at the parent
material, or bedrock. The topmosthorizons have the most organic matter, as
vegetation both above and below ground begin to decompose. Thenutrients from
the organic matter leach through the horizons with rainfall and other weathering
agents, causing the color changes you can see.
Vertical sectionof earth crust (~6 feet) – soil profile.
• Structure, thickness, consistency, texture, porosity, colour, chemical
composition.
• Soil profile vary from place to place
• Depends on climate, vegetation and parent rock
• Top soil thicker in forest
Layers of soil is Horizons- 6 horizons.
1) O-horizon (organic horizon or litter zone)
2) A-horizon (top soil)
3) B-horizon (sub soil)
4) C-horizon (weathering rock)
5) D-horizon (weathering rock)
6) R-horizon (bed rock)

2. SoilProfile
O-horizon: litter zone
a) Fresh or partially decomposed organic matter
b) Rich in saprophytic, fungi, bacteria, protozoa
c) Undergo changes soil temp, moisture
d) Present in forest, absent in desert, grassland & cultivated land.
A-horizon: top Soil
It a top soil- Zone of eluviation (leaching)
A1-horizon:
• Rich in humus, dark coloured.
• rich in organic material mixed with mineral soil

3. SoilProfile
• rich in bacteria and fungi
A2-horizon:
• zone of maximum leaching
• Less humus, light coloured
• Silicates, clays, iron oxide, aluminium oxide are removed
A3 horizon: it is transitional zone to the subjacent B-horizon
B-horizon: zone of illuviation (collection of materials)
• Consists of B1, B2, B3 – precipitation of transported materials
• Firm zone, granular or prismatic structure,
• deep coloured with aluminium, iron and organic colloids
• Rich in clay, roots of shrubs and trees reach up to this horizon.
C-horizon: weathering rock
Thick and contains large masses of weathered mineral materials
Zone G- water logged, low oxygen, grey layer
Zone Cc- rich with calcium carbonate
Zone Cs- rich with calcium sulphate,
Cc-s zones Characteristic of grassland
D-horizon: weathering rock
Rocks in active weathering state.
R-horizon: (bed rock)
Lowermost layer parental rockfrom which layers of soil are derived