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In this lesson we are going to discuss about the soil profile and its importance

Answer Text:
Soil Profile
- Vertical arrangement of different soil layers from the surface to the bed rock.
A mature soil is one with a fully developed profile while a young soil is one with a not fully developed profile.
Superficial layer
- Dry decaying organic matter covering the soil surface.
Horizon ‘A’
- Lies under a mat of surface vegetation and raw humus.
- Darker due to high humus content.
- Contains most of plant nutrients.
- Where most plant roots are found.
- Contains active micro organisms which breakdown organic matter into humus.
Horizon ‘B’
- Lies below top soil.
- Has small spaces between particles and hence less aerated.
- Has a hardpan or layer impeding drainage.
- Where most materials washed from horizon A have accumulated.
Horizon ‘C’
- Lies below sub soil.
- Made of partly mechanically weathered rock.
- Product of bed rock or may have been transported.
Horizon ‘D’
- Solid underlying rock.
- May have ponds of water which can be used by deep rooted plants during dry season.
Importance of Soil Profile
a) Determines the crops to be planted i.e. mature soils favour deep rooted crops while young soils favour shallow rooted crops.
b) Bed rock determines the chemical properties of the soil such as PH and nutrients.
Soil Catena

- Arrangement of soil on a mountain slope from top to bottom.

Factors Influencing Development of a Soil Catena
a) Relief
- On steep slopes there is high rate of erosion resulting in thin soils while on gentle slopes rate of weathering and erosion is balanced resulting
in thick soils.
- On flat areas such as valley floors where there is deposition there are peat or alluvial soils.
b) Drainage
- First drainage at mountain tops results in thin stony immature soils.
- Poor drainage in flat areas results in peat or alluvial soils.
c) Transportation of Debris
- Surface runoff transports sediments to lower gentle slopes where it accumulates forming deep colluvial soils
while thin stony immature soils with little organic matter called xeromorphic soils are left on steep slopes.