Soil Profile Chapter 8 PDF

Chapter 8 SOIL PROFILE A vertical section of soil through all horizons upto the parent material is termed as “Soil profile”. Pedon: It is small basic entity and smallest volume that can be classified as a “soil”. It is very similar to soil profile but three dimensional. Polypedon or soil i...

Chapter 8 SOIL PROFILE A vertical section of soil through all horizons upto the parent material is termed as “Soil profile”. Pedon: It is small basic entity and smallest volume that can be classified as a “soil”. It is very similar to soil profile but three dimensional. Polypedon or soil individual: Soil individual is collection of the similar types of pedons bound on all sides. Soil horizon: It is a layer of soil, approximately parallel to the soil surface, differing in properties and characteristics from layers below or above it. Soil profile is an historic record of all the soil forming processes. Five master horizons are recognized in soil profile and are designated using capital letters O, A, E, B and C. Soil horizons are two types 1. Genetic horizon 2. Diagnostic horizon Genetic horizons are classified as three categories a) Master horizons b) Transitional horizons or combination horizons c) Subordinate distinction within master horizons a) Master horizons: The capital letters are used to represent master horizons.  O- Horizons: (Organic) It comprises of organic horizons that form above the mineral soil. They result from litter derived from dead plants and animals. ‘O’ horizons usually occur in forest areas and are generally absent in grassland / normal soils.  A - Horizon: It is the top most mineral horizon. It contains a strong mixture of decomposed organic matter, which tends to impart a darker color than that of the lower horizons.  E - Horizon: It is an elluvial horizon. Clay and sesquioxides are leached out, leaving resistant minerals such as quartz. It is also called as washing out horizon  An ‘E’ horizon is generally lighter in color than the ‘A’ horizon and is found below ‘A’ horizon.  “B” – Horizon : It is an illuvial horizon. The deposition of materials washed out from A horizon to B horizon. It is considered layer of accumulation or illuviation. It is also called as washing in horizon  ‘C’ – Horizon: It is layer of parent material horizon.It is the unconsolidated material underlying the ‘Solum’ (A & B horizon). The ‘C’ horizon is out side the zones of major biological activities and is generally little affected by the processes that formed the horizons above it.  ‘R’- Layer : Underlying consolidated rock, with little evidence of weathering. b) Transtional horizons: The horizons having dominated properties of one master horizon but sub-ordinate properties of other. Ex: AB, EB and BE. An AB horizons has characters of both A and B horizons, but more like A horizon than B horizon. c) Sub – Ordinate Distinctions with in Master Horizons: p: plough layer disturbance h : illuvial accumulation of organic matter t :accumulation of silicate clays ss: presence of slickensides 2. DIAGNOSTIC HORIZONS A diagnostic horizon is one, which is formed as a result of pedogenic processes and having distinct properties or features that can be measured in terms of measurable soil properties. Based on the location in the soil profiles, these are divided into two categories. a. Diagnostic surface horizons (epipedons) b. Diagnostic sub -surface horizons (endopedons) Epipedons: Greek epi means over and pedon means soil Nine epipedons are recognized.  Mollic (L. mollis, soft) Epipedon  Umbric (L. umbra, shade) Epipedon  Anthropic (Gr. Anthropos, man made) Epipedon  Plaggen (Ger. Plaggen, sod) Epipedon  Ochric (Gr. ochros, pale) Epipedon  Histic (Gr. histos, tissue) Epipedon  Melanic (Gr. melanas, black) Epipedon  Folistic (L. folia, leaf) Epipedon  Grossarenic Epipedon (L.grossus, thick, arean, sand) [L. means Latin, Gr. Means Greek and Ger. Means German] 1. Mollic Epipedon: It has High >50 % base saturation. This epipedon is not naturally dry in all months for more than 9 months in a year. 2.Umbric Epipedon: It has all properties of mollic epipedon except base saturation is < 50%. 3. Antropic Epipedon: A surface horizon formed under continuos system of farming or cultivation having large amount of organic matter. 4. Plaggen Epipedon: The plaggen epipedon is a human made surface layer. It can be easily identified by bits of pottery or brick. It also shows spade marks. 5. Ochric Epipedon: A surface horizon that is light in colour. It has less than 1% organic matter. 6. Histic Epipedon: It is saturated for 30 days or more. 7. Folistic Epipedon: Saturated for < 30 days 8. Melanic Epipedon: This horizon is commonly formed on volcanic ash deposits. It has andic soil properties. 9. Grossarenic Epipedon: It has sandy texture of thickness 100cm or more. DIAGNOSTIC SUB-SURFACE HORIZONS (ENDOPEDONS) Formed below the surface of soil. Some of these are regarded as ‘B’ horizons and others as part of ‘A’ horizon. 19 endopedons are recognized..