Soil Classification

Soil Classification

The division of soils into classes according to their features of formation. One of these classes is the ancient soil classification, and the other is the soil taxonomy, which was made in 1975 and is constantly updated and performed according to the series. In the old soil classification system, which was made in 1930 and updated in 1960, soils are divided into three teams: 

1-zonal, 2-azonal and 3-intrazonal, and each team is divided into large soil groups.

Soil classification is the systematic arrangement of soils into different categories based on their properties, such as texture, structure, composition, and behavior under various environmental conditions. Classification helps in understanding the suitability of soils for various land uses, such as agriculture, construction, and conservation. Different systems are used worldwide for soil classification, but the two most widely recognized are the USDA Soil Classification System and the World Reference Base for Soil Resources (WRB).

1. USDA Soil Classification System

The USDA Soil Taxonomy is one of the most commonly used systems for classifying soils in the United States and many other parts of the world. It classifies soils based on their physical, chemical, and biological properties into 12 soil orders, which are then further divided into suborders, great groups, subgroups, families, and series.

The 12 Soil Orders (Main Categories) in USDA Classification:

1. Alfisols:

   • Characteristics: Fertile soils found in temperate forests. They are rich in clay minerals and have a moderate level of base saturation.
   • Location: Found in humid and subhumid climates.
   • Use: Suitable for agriculture, particularly in crops like wheat, corn, and soybeans.

2. Andisols:

   • Characteristics: Volcanic soils that are rich in minerals like aluminum and iron. They are highly fertile, especially for growing crops.
   • Location: Common in volcanic regions (e.g., Pacific Islands, Indonesia).
   • Use: Ideal for intensive farming, especially in crops like coffee, rice, and vegetables.

3. Aridisols:

   • Characteristics: Soils of dry regions with limited moisture and vegetation. They often have a high content of salts.
   • Location: Found in deserts and semi-arid regions.
   • Use: These soils require irrigation for successful agriculture and may be suitable for growing drought-resistant crops.

4. Entisols:

   • Characteristics: Young soils with little horizon development, often found in floodplains or sandy areas.
   • Location: Found in areas with recent deposits of sediment.
   • Use: Can be used for agriculture but need proper irrigation and management.

5. Gelisols:

   • Characteristics: Soils found in very cold climates, typically frozen or permafrosted. They may have frozen layers that restrict root growth.
   • Location: Common in polar regions, such as the Arctic.
   • Use: Limited agricultural potential due to cold conditions.

6. Histosols:

   • Characteristics: Organic soils rich in decomposed plant material (peat). They are usually waterlogged and can store a lot of water.
   • Location: Found in wetlands, bogs, and marshes.
   • Use: Suitable for crops that thrive in wet conditions, such as rice or cranberry bogs.

7. Inceptisols:

   • Characteristics: Soils with weak horizon development, but better than Entisols. They are found in a variety of climates and landscapes.
   • Location: Found in areas of moderate rainfall and temperature.
   • Use: Used for agriculture and forestry in moderate climates.

8. Mollisols:

   • Characteristics: Fertile soils with a dark, organic-rich surface horizon. These are excellent for growing a wide range of crops.
   • Location: Found in grassland ecosystems, such as the prairies of North America.
   • Use: Ideal for farming, particularly for crops like wheat, corn, and vegetables.

9. Oxisols:

   • Characteristics: Highly weathered soils found in tropical regions. They are rich in iron and aluminum oxides but low in nutrients.
   • Location: Common in tropical rainforests.
   • Use: Can be used for farming but require soil amendments for high productivity.

10. Spodosols:

• Characteristics: Soils that develop in cold, wet climates. They have a distinctive layer of leached material (podzol horizon).
• Location: Found in boreal forests and northern climates.
• Use: Limited agricultural potential due to acidity, but can support certain crops like potatoes.

11. Ultisols:

• Characteristics: Highly weathered soils with low fertility and high acidity, often found in warm, humid climates.
• Location: Found in tropical and subtropical regions.
• Use: Require soil amendments for agriculture, particularly for growing crops like rice, cassava, and sugarcane.

12. Vertisols:

• Characteristics: Clay-rich soils that shrink and swell with moisture changes. They are prone to cracking during dry conditions.
• Location: Found in regions with seasonal rainfall, particularly in semi-arid areas.
• Use: Suitable for crops like cotton, beans, and cereals.

2. World Reference Base for Soil Resources (WRB)

The WRB is an international soil classification system developed by the Food and Agriculture Organization (FAO). It focuses on soil properties and their suitability for land use, agriculture, and conservation.

The Main Categories in WRB:

1. Chernozem:

   • Characteristics: Very fertile, black soils rich in organic matter, similar to Mollisols in the USDA system.
   • Location: Found in grasslands and temperate regions.
   • Use: Excellent for agriculture, particularly for wheat and other grains.

2. Phaeozem:

   • Characteristics: Dark, fertile soils with a high organic matter content, similar to Chernozem but with a different mineral composition.
   • Location: Found in temperate regions, especially in the steppe.
   • Use: Ideal for agriculture and forestry.

3. Gleysol:

   • Characteristics: Soils that develop under waterlogged conditions, often with a significant amount of organic material.
   • Location: Found in wetland areas.
   • Use: Used for crops that thrive in wet environments, such as rice.

4. Andosol:

   • Characteristics: Volcanic soils with high mineral content and good fertility.
   • Location: Found in volcanic regions.
   • Use: Ideal for intensive agriculture due to high fertility.

5. Regosol:

   • Characteristics: Young, poorly developed soils that are usually shallow and found on recent deposits of material.
   • Location: Found in a variety of landscapes, including floodplains and mountains.
   • Use: Can be used for agriculture but often require soil amendments.

3. Other Soil Classification Systems

• FAO/UNESCO Soil Classification System: This is a widely used system for classifying soils based on their diagnostic horizons, properties, and their ability to support agriculture. The FAO/UNESCO system uses categories like Alfisols, Andosols, Gleysols, and more.

• Australian Soil Classification System: This system is used to categorize soils in Australia and includes orders such as Ferrosols, Chromosols, and Dermosols. It is closely related to the USDA and WRB systems.

Conclusion

Soil classification helps in determining the best management practices for different soil types based on their properties. Different classification systems, such as the USDA Soil Taxonomy and WRB, provide valuable frameworks for understanding soil behavior, fertility, and land suitability. Understanding the classification of the soil in a particular region is essential for choosing the right plants, crops, and management practices to ensure sustainable land use and agricultural productivity.