The World Soil Classification of Curtis Fletcher Marbutt (1863–1935) is one of the best-known soil classifications. He emphasized the strong relationship between climate, vegetation, and soil in his soil classification.

As per Marbut, world soil can be classified into three major classes:

• Zonal Soil Group
• Intrazonal Group
• Azonal Soil Group

1. Zonal Types

These soils occur in broad geographical areas or zones.The influence of the climate and vegetation of the area on them is greater than that of the rock-type. They are mature, as a result of stable conditions over a long period of time.

• Podzols (ash-soil)
• Brown Earth
• Tundra Soils
• Sierozems
• Chernozem Soils
• Chestnut soils
• Prairie soils
• Grumusols
• Ferralsols

2. Intrazonal Types

These soils occur within other zonal soils. It is a well-developed soil reflecting the influence of some local factor of relief, parent material, or age rather than of climate and vegetation.

• Hydromorphic soils
• Calcimorphic soils
• Halomorphic (saline) soils

3. Azonal Soils

Agents of erosion have deposited soil by transporting fine rocky particles from far-off regions, resulting in its development. These are immature soils and lack well-developed soil profiles. This may be due to the non-availability of sufficient time for them to develop fully or due to the location on very steep slopes which prohibits profile development.

• For example, on active flood-plains, alluvial soils have little or no profile development, because of their frequent burial under new sediments;
  • Alluvial Soil;
    • It is developed by river deposits.
    • Distribution of Alluvial Soil is in:
    • Northern plain of India
    • Eastern North America
    • Eastern China
    • Southeast Asia except for Indonesia and Malaysia
• Regosols are compose of dry and loose dune sands or loess.
• Accumulations of imperfectly weathered rock fragments on steep slopes, where erosion rates remove soil almost as fast as it forms, give rise to lithosols.

Soil Taxonomy

Soil Taxonomy classifies soils based on their physical and chemical properties, including texture, structure, color, and mineralogy. Soils are also classified based on the factors that influence their formation, including climate, parent material, topography, and biota.

Soils are classified into twelve orders in the Soil Taxonomy system, with each order representing a distinct set of soil properties and formation factors. The12 orders are:

• Entisols: These soils have a lack of horizon development and are typically found in young soils or areas with frequent disturbances.
• Inceptisols: These soils have a weakly developed horizon and are found in areas with moderate soil development.
• Andisols: These soils are derived from volcanic ash and have unique physical and chemical properties.
• Gelisols: These soils are found in areas with permafrost, and they exhibit the presence of frozen soil layers.
• Histosols: These soils are organic-rich and are typically found in wetland areas.
• Aridisols: These soils are found in dry, arid areas and are characterized by low organic matter content.
• Mollisols: These soils are found in grassland areas and are characterized by a thick, dark-colored surface horizon.
• Alfisols: Areas with moderate to high rainfall are where these soils are found, and they are characterized by a subsurface clay horizon.
• Ultisols: These soils are found in areas with high rainfall and are characterized by a subsurface clay horizon and low base saturation.
• Spodosols: These soils are found in areas with high acidity and are characterized by a subsurface layer of iron and aluminum compounds.
  Oxisols: These soils are found in tropical regions and are characterized by a highly weathered, deep profile.
• Vertisols: These soils have a high content of expandable clay and are characterized by high shrink-swell potential.

Soil classification based on climate

1. Arid Soils: These soils form in arid or desert climates with low precipitation and high evaporation rates. They are typically sandy and have limited organic matter content.
2. Semi-arid Soils: These soils occur in semi-arid regions with moderate precipitation and evaporation rates. They have variable textures and may contain more clay and organic matter compared to arid soils.
3. Subtropical Soils: Subtropical regions, which have warm and humid climates, are where these soils are found. They undergo high weathering and may exhibit distinct horizons. These soils can vary in texture and fertility.
4. Tropical Rainforest Soils: In regions with high rainfall and high temperatures, tropical rainforest soils undergo leaching and exhibit characteristics of being nutrient-poor with a thin organic layer.
5. Temperate Soils: In temperate climates with moderate precipitation and temperatures, these soils occur as generally well-drained and fertile, making them suitable for agriculture.
6. Boreal Soils: These soils are found in boreal or taiga regions, which are characterized by cold temperatures and moderate to low precipitation. They are often acidic and may have a high organic matter content.
7. Polar Soils: These soils occur in polar regions with extremely cold temperatures and low precipitation. They are typically shallow, frozen, and have limited organic matter.

Frequently Asked Questions related to the classification of soils on Earth:

Ques 1. How are soils classified?

Ans. Soils are classified based on various factors, including their composition, texture, fertility, and other properties. Different classification systems, such as the USDA soil taxonomy or the World Reference Base for Soil Resources, categorize soils into groups and subgroups based on specific criteria and characteristics.

Ques 2. Why is soil classification important?

Ans. Soil classification provides a standardized system for organizing and categorizing soils, allowing for better understanding and communication among scientists, land managers, and agricultural practitioners. It helps in assessing soil fertility, suitability for different land uses, and making informed decisions regarding soil management and conservation.

Ques 3. What are the main soil classification categories?

Ans. Soil classification categories typically include factors such as soil texture (e.g., clay, silt, sand), organic matter content, pH level, mineral composition, and drainage properties. Soils may be classified into different groups, such as loam, clayey, sandy, peaty, or silty, based on their dominant characteristics.

Classification of Soils on Earth,Classification of Soils on Earth,

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