Get premium membership and access revision papers with marking schemes, video lessons and live classes.

Processing. Please wait.

In this lesson we are going to discuss about soil formation processes

Answer Text:
Soil Formation
Factors Influencing Soil Forming Processes
a) Parent Material
- Determines the type of soil, mineral composition and texture e.g. granite and sandstone weather to form
sandy soils rich in quartz, volcanic lavas form clay soils with low quartz content and plants decompose to form
loam rich in humus.
b) Climate
- Affect rate and type of weathering e.g. heavy rainfall results into deep soils due to heavy weathering and leaching.
- Wind in deserts causes formation of loess soils.
c) Living Organisms
- Micro-organisms such as bacteria cause plant and animal remains to decay into humus.
- Burrowing animals and worms mix organic remains with mineral soil component.
- Roots penetrate and add more porosity, improve soil depth and aeration.
d) Topography
- There is maximum soil development in rolling and well drained uplands where the rate of erosion matches that of soil erosion.
- Steep slopes result in shallow immature soils due to severe erosion.
Time
- The longer the time taken by soil forming processes the deeper and well developed soil is.
Soil Forming Processes
1. Weathering
- Breakdown of parent rock to form rock particles called regolith.
2. Decomposition of Organic Matter
Processes
a) Mineralization
- Biological and chemical breakdown of dead plant tissues by soil microorganisms to simple soluble organic substances.
b) Humification
- Regrouping of mineralized dead plant material into large molecules to form humus.
3. Leaching
- Carrying of minerals from top layer down to the middle layer.
Types
i) Ferralisation/lateralisation
- Moving in solution or in suspension of weathered material from horizon “A” to “B.”
- Red soil form in horizon A as ferrisols/laterites (murrum).
ii) Illuviation
- Accumulation/redeposition of materials which had been leached to horizon B.
- Hard soil mass (hard pan) results.
iii) Eluviation
- Mechanical washing down of fine mineral particles in suspension from upper layer to lower layers by water which
is percolating downwards. e.g. clay
iv)Podzolisation
- Heavy depletion of horizon A of all minerals especially bases and iron by soluble organic substances.
- Forms ash like soils which are acidic.
v) Calcification
- Limited leaching which allows redeposition of calcium compounds within the same soil profile.
vi) Ribification
- Dehydration of soils during dry season and leaching during the rainy season.