2. SOIL GENESIS, PHYSICAL, CHEMICAL AND COLLOIDAL PROPERTIES OF SOIL

3. Soil Genesis
Genesis means origin. It means how soils are developed. Mostly soils are developed by weathering of minerals. Soil genesis includes soil forming factor and soil forming process.
Soils from mineral materials are developed by the dynamic forces of climate and the action of plants and animals (biosphere) as modified by topography (lay of the land) over time (years).

4. I- RESIDUAL PARENT MATERIALS:
Parent material formed from weathered minerals
Weathering of bed rocks
R.P.M. is formed on relatively level topography
ORIGIN OF PARENT MATERIAL:
may be from rocks
Igneous
Sedimentary
Metamorphic rocks—chemical composition changed by heat

5. II- TRANSPORTED PARENT MATERIAL: formed from weathered rocks that have been moved to another location by water, wind, ice or gravity.
III- CUMULOSE PARENT MATERIAL:
Could be called residual parent material
Because they have been formed in place, in another sense, they are not residual because they did not develop from underlying bed rocks.
Parent material of organic soils (cummulose) are mostly plant residues preserved by excessive soil wetness.

6. SOIL FORMATION FACTORS
A soil is generated when the active factors of climate and biosphere interact with passive parent material and modified by passive topography over neutral time.
Parent material
Climate
Organisms
Topography
Time

7. Soil Forming Processes
Boul et al. (1980). Lists a number of important soil forming processes into four categories i.e. additions, losses, transfers and transformation with in a soil body. Further these are classified as
General processes
Specific processes

8. General Soil Forming Process
Eluviation: movement of material out (e.g., E horizons; also A horizons).
Illuviation: movement of material in (B horizons)
Decalcification: removal of calcium carbonate
Lessivage: downward migration and accumulation of clay, producing an argillic or clay-enriched horizon.

9. Fullerton Series, Typic Hapludult, showing clay, Fe accumlation in the Bt horizon.

10. Pedoturbation
Pedoturbation is the process of soil mixing by fauna and flora and physical churning and cycling of soil materials. It may invert soil layers. It has following types
Faunal Pedoturbation
Floral Pedoturbation
Agrilli Pedoturbation

11. Specific Soil Forming processes
Calcification
Weak eluviation and formation of secondary calcium carbonates in sub soil horizons and leads to formation of the chernozemic soils.

12. Podzolization
Fe, Al, and organic matter accumulate in the illuviated spodic (Bh or Bs)
Fe and Al leach from eluviated albic (E) horizon
Dominant in the boreal climatic zone,
Also occur in southeast coastal plain of US (Aquods, Groundwater Podzols) an
“Giant podzols'' with extremely thick E and Bs horizons occur in the tropics

13. Other Specific Soil Forming Process
Salination
Alkalization
Desalination
Dealkalization

14. Spodosol: a result of podzolization (called Podzols in other classification systems besides the US)
Photo of soil profile
Photos courtesy of USDA NRCS, National Survey Center

15. CLIMATE AND SOIL GENESIS
SOIL ORDERS
Entisols (any climate, young parent material)
Aridisols (dry climate)
Histosols (any climate where surface water is abundant)
Oxisols (tropical climate)
Ultisols (humid, sub-tropical climate)
Mollisols & Vertislos (calcareous plant material)
Alfisols & Inceptisols (not closely related with climate)
Spodosols

16. Aridisol Entisol Photos courtesy of USDA NRCS, National Survey Center

17. Gelisol Histosol Photos courtesy of USDA NRCS, National Survey Center

18. Inceptisol Mollisol
Photos courtesy of USDA NRCS, National Survey Center

19. Oxisol Spodosol Photos courtesy of USDA NRCS, National Survey Center

20. Ultisol Vertisol Photos courtesy of USDA NRCS, National Survey Center

21. Topography and soil genesis
Determines runoff water
Controls the amount of soil material removed and relocated
Affects deposition and soil texture
Affects the vegetation

22. Biosphere and soil genesis
Flora + Fauna
Active Factor
Effect of plants
Effect of animals

23. Time and soil genesis Affects soil genesis Neutral Factor
Time influences all other factors

24. Soil Physical Properties
Soil Texture
Provides general information regarding the amount of sand, silt and clay
Soil Structure
Arrangement of soil particles to form aggregates

25. Soil Physical Properties
Soil Consistence
Relative cohesive strength of aggregates to resist rupture and deformation.
Particle density
Weight of individual soil particle in relation to water
Bulk density
Weight of volume of soil in relation to equal volume of water

26. Soil Physical Properties
Soil Color
Measured in terms of hue, value and chroma

27. Soil Physical Properties
SOIL TEMPERATURE
Bacteria (25-30 oC)
Fungi (37 oC)
N Fixing Organisms (36 oC)
Actinomycetes (55-59 oC)

28. Soil Chemical and colloidal Properties
Organic Matter
Provides a generalized indication of the relative fertility status of soil, promotes great water retention, aeration and fertility.
Soil pH
An index of the relative acidity and alkalinity of the soil.
Buffering
Resistance to change in pH

29. Soil Chemical and Colloidal Properties
Soil Salinity Range
An index of salt content
Cation Exchange Capacity
Relative measure of soil potential to retain added nutrients