soil genesis, physical, chemical and colloidal properties of soil
TRANSCRIPT
SOIL GENESIS, PHYSICAL, CHEMICAL AND COLLOIDAL
PROPERTIES OF SOIL
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).
I- RESIDUAL PARENT MATERIALS: Parent material formed from weathered
minerals Weathering of bed rocks R.P.M. is formed on relatively level
topographyORIGIN OF PARENT MATERIAL: may be from rocks1. Igneous2. Sedimentary3. Metamorphic rocks—chemical composition
changed by heat
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.
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
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
General Soil Forming ProcessGeneral Soil Forming Process
• Eluviation:Eluviation: movement of material out (e.g., E movement of material out (e.g., E horizons; also A horizons). horizons; also A horizons). •Illuviation:Illuviation: movement of material in (B horizons) movement of material in (B horizons) •Decalcification:Decalcification: removal of calcium carbonate removal of calcium carbonate •LessivageLessivage: downward migration and accumulation : downward migration and accumulation of clay, producing an of clay, producing an argillicargillic or clay-enriched or clay-enriched horizon.horizon.
Fullerton Series, Typic Hapludult, showing clay, Fe accumlation in the Bt horizon.
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
Specific Soil Forming processesSpecific Soil Forming processes
CalcificationCalcification
Weak eluviation and formation of secondary Weak eluviation and formation of secondary calcium carbonates in sub soil horizons and calcium carbonates in sub soil horizons and
leads leads to formation of the chernozemic soils.to formation of the chernozemic soils.
PPodzolizationodzolization
Fe, Al, and organic matter accumulate in the Fe, Al, and organic matter accumulate in the illuviated spodic (Bh illuviated spodic (Bh or Bs) or Bs)
Fe and Al leach from eluviated albic (E) Fe and Al leach from eluviated albic (E) horizonhorizon
Dominant in the boreal climatic zone,Dominant in the boreal climatic zone, Also occur in southeast coastal plain of US Also occur in southeast coastal plain of US
(Aquods, Groundwater Podzols) an(Aquods, Groundwater Podzols) an ““Giant podzols'' with extremely thick E and Giant podzols'' with extremely thick E and
Bs horizons occur in the tropicsBs horizons occur in the tropics
Other Specific Soil Forming Process
Salination Alkalization Desalination Dealkalization
Photo of soil profile
Spodosol: a result of podzolization (called Podzols in other classification systems besides the US)
Photos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
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
Aridisol Entisol
Photos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Gelisol Histosol
Photos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Inceptisol Mollisol
Photos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Oxisol Spodosol
Photos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Ultisol Vertisol
Photos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Topography and soil genesis Determines runoff water Controls the amount of soil material
removed and relocated Affects deposition and soil texture Affects the vegetation
Biosphere and soil genesis Flora + Fauna Active Factor Effect of plants Effect of animals
Time and soil genesis Affects soil genesis Neutral Factor Time influences all other factors
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
Soil Physical Properties Soil Consistence
Relative cohesive strength of aggregates to resist rupture and deformation.
Particle densityWeight of individual soil particle in relation to water
Bulk densityWeight of volume of soil in relation to equal volume of water
Soil Physical Properties Soil Color Measured in
terms of hue, value and chroma
Soil Physical Properties
SOIL TEMPERATURE Bacteria (25-30 oC) Fungi (37 oC) N Fixing Organisms (36 oC) Actinomycetes (55-59 oC)
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
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