CLASSIFICATION OF SOIL PARENT MATERIALS Igneous rocks SEDIMENTARY

CLASSIFICATION OF SOIL PARENT MATERIALS

Igneous rocks

SEDIMENTARY ROCKS

METAMORPHIC

Soil Development by 3 processes 1 - Mechanical disintegration (weathering or erosion) water Temperature Wind 2 - Chemical decomposing (a) Oxidation (e) Carbonation (b) Reduction (c) Hydration (F) Solution 3 - Biological activity decomposing Soil animals Soil Microorganisms (d) Hydrolysis

SOIL FORMATION 1 - Mechanical (disintegration) processes

1) Oxidations: Sulfur compounds are oxidized in soils to sulfuric acid SO 3 + H 2 O H 2 SO 4, Fe+++ 2) Reduction: In water logged soil, ferric irons are reduced to ferrous form Fe+++ Fe++ 3) Hydration causes physical disintegrate of rock because the hydrated compounds occupy more space and play an active role in weathering 2 Fe 2 O 3+ 3 H 2 O 2 Fe 2 O 3. 3 H 2 O

4) Hydrolysis This process goes on extensively with minerals containing strongly basic elements parts of which are exchanged for Hydrogen Ca. Si. O 3 + 2 H 2 O Ca(OH)2 + H 2 Si. O 3 5) Carbonation The decomposition of organic mater in the soil and the respiration of plant roots liberate large quantities of CO 2 in the soil air. This gas readily combines with bases, producing carbonates or bicarbonates. Carbonic acid is also formed and acts on rocks. Ca(OH)2 + CO 2 Ca(HCO 3)2 6) Solutions occur in soil in the form of acids e. g. HNO 2; H 2 SO 4; HCO 3 etc These acids are developed in soil through chemical and biological agencies

SOIL PROFILE - Downward section in soil - 3 layers result from weathering