Classification and Distribution of Soils in India: Types, Features, and Regions.

Classification and Distribution of Soils

• Soil Classification
  • Soil classification is complex, aiming to be meaningful to geographers while accurately reflecting soil types and gradations.
  • Two main types of classification are used:
    • Based on the assumed origins of the soil.
    • Based on the observable properties of the soil profile.



• Zonal System
  • The zonal system was proposed by Russian pedologists (Dukuchaiev, Glinka) and highlights the relationship between climate, vegetation, and soil zones.
  • Three main classes of soils are recognized:
    • Zonal soils: Well-developed soils reflecting climate as the dominant factor.
    • Intrazonal soils: Well-developed soils formed due to dominant local factors.
    • Azonal soils: Immature or poorly developed soils.



• Zonal Types
  • Zonal soils occur in broad geographical areas and are influenced by climate and vegetation more than rock type.
  • Examples include:
    • Podzols (ash-soil): Characterized by a bleached E horizon due to cheluviation. Found in cool climates south of the tundra region, often associated with coniferous forests.
    • Brown Earth: Found in milder climates supporting deciduous forests. These soils exhibit less intense leaching compared to podzols and have a brown color due to dispersed sesquioxides.
    • Tundra Soils: Variations exist due to patterns of ground ice. Examples include brown polar desert soils and Arctic brown forest soils.
    • Sierozems: Found in desertic areas with low organic matter but high fertility when irrigated.
    • Chernozem Soils: Found in steppe or prairie regions. They have a calcium-rich horizon and a deep dark upper layer with high humus content.
    • Chestnut Soils: Located in the arid side of the chernozem belt, these soils have a lower organic content and shallow carbonate layers.
    • Prairie Soils: Found in the transition zone between chernozems and forest brown earth.
    • Grumusols: Dark clayey soils in savanna regions with seasonal wet and dry climates, characterized by dry-season cracking.
    • Ferralsols: Tropical soils rich in ferric oxide, with low fertility due to the lack of humus and bases.
• Intrazonal Types
  • Intrazonal soils occur within zonal soil types and reflect the influence of local factors like relief, parent material, or age.
  • Examples include:
    • Hydromorphic Soils: Found in marshes and swamps, these soils undergo gleying due to waterlogging.
    • Calcimorphic Soils: Developed on calcareous parent material. Examples include rendzinas (rich in organic matter) and terra rossa (clay-rich and reddish in color).
    • Halomorphic (saline) Soils: Found in deserts with types such as solanchak, solonetz, and solodic soils.

    

• Azonal Soils
  • Azonal soils are immature soils developed through deposition by agents of erosion and lack a well-developed profile.
  • Examples include:
    • Alluvial Soils: Found on active floodplains, these soils are frequently buried under new sediments.
    • Regosols: Composed of dry, loose dune sands or loess.
    • Lithosols: Found on steep slopes, consisting of imperfectly weathered rock fragments.
  • Criticisms of the zonal concept:
    • Zonal soils can exist outside their typical climate zones.
    • Azonal soils may be influenced by local factors, not just the lack of time for development.
    • Soil profiles may reflect past climates rather than current conditions.

• USDA Soil Taxonomy
  • The US Department of Agriculture uses a soil classification system based on observed soil properties rather than genetic considerations.
  • Twelve orders of soils are identified based on their developmental properties and the presence or absence of diagnostic horizons.
  • Alfisols: Named for aluminum and iron content.
  • Andisols: Soils derived from volcanic ash.
  • Aridisols: Soils typical of arid climates.
  • Entisols: Recently formed soils lacking distinct horizons.
  • Gelisols: Found in regions with permafrost.
  • Histosols: Soils rich in organic matter.
  • Inceptisols: Young soils with weakly developed horizons.
  • Mollisols: Known as grassland soils with high fertility.
  • Oxisols: Found in tropical regions, rich in oxygen compounds.
  • Spodosols: Characterized by ashy horizons.
  • Ultisols: Leached soils with low nutrient bases.
  • Vertisols: Expansive soils formed from volcanic rock.
• Soils Characterized by Maturity

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  • Entisols: Mineral soils with no distinct horizons, recently deposited, found in equatorial to arctic zones.
  • Inceptisols: Weakly developed horizons, found in river floodplains and deltas, highly productive in warm, moist climates.
• Soils Characterized by Climate
  • Mollisols: Grassland soils with high fertility and a thick mollic epipedon, found in the Great Plains, Pampas, and Eurasian steppes.
  • Aridisols: Desert soils with calcium carbonate layers, fertile with irrigation.
  • Gelisols: Permafrost soils churned by freeze/thaw action, rich in organic matter.
• Soils Characterized by Parent Materials
  • Vertisols: Formed on volcanic rock, expansive, found in the Deccan Plateau of India.
  • Andisols: Derived from volcanic ash, typically fertile, supporting dense vegetation in moist climates.
• Soils High in Organic Matter
  • Histosols: Known as peat or muck soils, formed in cool, poorly drained climates, rich in organic matter.
• Specialized Soils
  • Alfisols: Found across diverse climates, from boreal forests to Mediterranean regions, characterized by clay-rich horizons formed through illuviation.
  • Spodosols: Acidic soils with light-colored albic horizons, commonly found under cold needle leaf forests.
  • Oxisols: Stable soils in equatorial regions, typically associated with rainforest ecosystems.
  • Ultisols: Vulnerable to soil erosion, found in regions like Southeast Asia, South America, and the United States.

• General Classification of Soil
  • The most comprehensive basis for the classification of soils is the specific climate and vegetation under which the soil has grown and developed.
  • Accordingly, the soils of the world can be broadly classified into two main types:
    • Pedalfurs
      • These soils have grown in humid areas under rich vegetation cover.
      • They contain a greater proportion of aluminium and iron but lack essential plant nutrients such as potassium, calcium, and phosphorus.
    • Pedocols
      • These soils have developed under arid conditions and retain all the elements needed to make plant foods.
      • They are found in regions receiving less than 25 inches of rainfall annually and are generally lighter in color.
      • Pedocols do not suffer from leaching and are alkaline in nature.
  • These two main soil classes have further subdivisions or sub-varieties based on:
    • The type of vegetation cover
    • Temperature conditions
    • The amount of precipitation