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 topography ORIGIN OF PARENT MATERIAL: may be from rocks Igneous Sedimentary 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 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.

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

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

Other Specific Soil Forming Process Salination Alkalization Desalination Dealkalization

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 http://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 Center http://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm

Gelisol Histosol Photos courtesy of USDA NRCS, National Survey Center http://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm

Inceptisol Mollisol Photos courtesy of USDA NRCS, National Survey Center http://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm

Oxisol Spodosol Photos courtesy of USDA NRCS, National Survey Center http://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm

Ultisol Vertisol Photos courtesy of USDA NRCS, National Survey Center http://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 density Weight of individual soil particle in relation to water Bulk density Weight 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