SOIL ORIGIN .ppt
- 1. SOIL ORIGIN AND NATURE, FORMATION OF SOILS
- 2. • Soil develops from parent material by the processes of soil formation • The process of formation soil from the hard rock (eg. granite) are divided into two stages – Rock weathering – Soil formation • The mineral matter inherited form rocks are referred to as soil parent material
- 3. • The principle parent materials of organic soils are formed due to decomposing of plant materials • The most important properties of parent’s materials are texture and mineral composition
- 4. • Rocks - formed by the cooling of a molton mass called magma • The most common igneous rocks are basalt and granite • Basalt rock - most common lava rock which is the principle hard rock underlying the ocean basins • Basalt rock due to weathering produces a large percentage of clay and less percentage of stone
- 5. • Granite rock - weathers to coarse grained rocks to produce much sandier soil • Granite usually produces a deeper soil than basalt • Igneous rocks – source - 10% of the earth soil area • The remaining 90% of the land area has a mantle of sedimentary or metamorphic rocks
- 6. SEDIMENTARY ROCKS • Are formed by the cementation of iron of materials deposited by wind, water, ice or gravity • Cementation is by iron, aluminum, silicon, CaCO3 etc) • Sedimentary rocks are shale, limestone, quartz stones etc
- 7. METAMORPHIC ROCKS • Are formed under heat and pressure • Sandstone can change to quartzite, shale to slate and limestone to marble
- 8. SOIL FORMATION • Weathering - responsible for the formation of the regolith and in turn the soil • Weathering - combination of destruction and synthesis • Simultaneously rock fragments and the minerals therein are attached by weathering forces • These changes are accompanied by a continued decrease in particle size and by release of soluble constituents.
- 9. PROCESS OF WEATHERING • Mechanical disintegration • Chemical decomposition I. Mechanical a. Temperature : differential expansions of minerals, frost betion and exfoliation. b. Erosion and deposition – by water ice wind c. Plant and animal influences
- 10. II. Chemical a. Hydrolysis b. Hydration c. Carbonation and related acidic processes d. Oxidation e. Solution
- 11. MECHANICAL FORCES OF WEATHERING Temperature • Sudden or wide variations of temperature influence the disintegration of rocks • Warming and cooling process are effective in disintegration of parent materials
- 12. • Freezing of water It widens the cracks and dislodges rocks to fragments • Water Water has a tremendous cutting power in the valleys of rivers • Ice Ice is an erosive and transporting agency which disintegrates rocks • Wind Wind always had been important transporting agent for dust storms • Plants Mosses and lichens produces organic materials - help in disintegration and the growth of roots in the rocks crevices and thus disintegration of rock
- 13. CHEMICAL PROCESS OF WEATHERING – DECOMPOSITION • Hydrolysis It is a decomposition reaction especially in case of feldspars & mica • Hydration It is the processes of attachment of H+ and OH- ions to the compounds 2 Fe2O3+3H2O 2 Fe2O3 H2O Hematite (red) Limonite (Yellow)
- 14. • Carbonation Hydrogen ion, carbonic acid, HNO3, H2SO4 CaCO3 + H2CO3 Ca(HCO3)2 Calcite Carbonic Acid Soluble Bicarbonate • Oxidation Fe++ Fe+++ 4FeO+O2 2Fe2O3 Ferrous Oxide Hematite
- 15. Solution Dissolved CO2 and H+ ions Fig. : How various kinds of parent’s material are formed transported & deposited
- 16. SOIL PARENT MATERIALS OR WEATHERED SOILS – Residual parent material – Alluvial debris – Alluvial stream deposits – Marine sediments – Lacustrine – Glacial – Eolian (Sand size) silt size- Transported by wind
- 17. FACTORS INFLUENCING SOIL FORMATION • Climatic condition - particularly temperature and precipitation • Living organism - especially native vegetation • Nature of parent material – Texture & structure of soil • Chemical & mineralogical composition of soil • Topography of the area • Time of soil formation
- 18. SOIL PROFILE • Horizontal distribution of soil layers are called soil horizons • The vertical sequence of soil horizons are termed as soil profile • Soil forming processes are grouped under four heads-O,A, Band C Consolidated bed rock.
- 19. • O Group: The organic horizons which lie above the mineral soil • A group: The mineral horizons which are at or near the surface characterized by maximum leaching • B Group: The layer in which deposition from above or even below • It is the region of maximum accumulation of materials such as oxides of iron and aluminum and silicate clays • These materials may have washed downward from the surface layers or they have formed in the B horizon • In the arid region calcium carbonate and calcium sulphate may be accumulated
- 20. • A & B horizon together is called the solum • C- Horizon: It is the unconsolidated material underlying the solution. Least weathered accumulation of Ca , Mg carbonate, cementation, some times high bulk density fragipans • R-Horizon: Consolidated bed rock. It may or may not be like the parent rock from which the solution is formed