Comprehensive Soil Classification System (1975)
Recognizing the limitations of earlier soil classification systems, the Soil Survey Staff of the US Soil Conservation Service developed an exhaustive and scientific classification scheme in 1975, known as Soil Taxonomy. This system aimed to classify the world’s soils systematically based on their composition, development, and weathering.
Key Features of Soil Taxonomy:
- Hierarchy-Based System: Soils are grouped into 10 orders, representing the highest level of classification.
- Scientific Criteria for Classification:
- Composition – Organic, mineral, or a combination.
- Soil Horizon Development – Degree of layering in the soil profile.
- Presence of Diagnostic Horizons – Specific layers that define soil properties.
- Weathering Intensity – Measured by Cation Exchange Capacity (CEC), which indicates nutrient retention ability.
The 10 Major Soil Orders:
| Soil Order | Key Characteristics |
| Alfisols | Mineral soils, low in organic matter, but with high base saturation. Contains a clay-rich horizon. Sufficient moisture for crops. |
| Aridisols | Dry-region mineral soils, low in organic matter. Well-developed horizons but require irrigation for crops. |
| Entisols | Young soils with no developed horizons. Found in diverse climates with variable moisture. |
| Histosols | Organic-rich soils, formed from decomposed plant matter. High water-holding capacity. |
| Inceptisols | Mineral soils with some horizon development but no illuvial clay layer. Moisture available for crops. |
| Mollisols | Highly fertile soils with a thick, dark organic-rich surface and high base saturation. Found in grasslands. |
| Oxisols | Highly weathered tropical soils, rich in iron and aluminum oxides, but low in minerals. |
| Spodosols | Acidic soils with an illuvial layer of aluminum and organic matter. Typically found in moist, well-leached areas. |
| Ultisols | Mineral soils with low base saturation and clay accumulation in humid climates. Less fertile than Mollisols. |
| Vertisols | Clay-rich soils that develop deep cracks during dry periods. Found in seasonally wet-dry areas. |
🧠 Mnemonic to Remember:
“All Amazing Earth Has Incredible Moist Organic Soil Under Very old Stones”
The first letter of each word is same as the soil type. In this way you may remember
Significance of Soil Taxonomy
- Global Applicability: Unlike earlier systems, this classification is scientifically structured to accommodate all types of soils worldwide.
- Practical Use: Helps in soil management, agriculture, and environmental planning.
- Scientific Rigor: Based on quantifiable properties rather than assumptions about climate-soil relationships.
This modern and systematic approach allows better understanding and management of soils, making it a widely accepted global standard for soil classification.
