Question

Black soils belong to which of the following order of soil classification?

• A. Vertisols
• B. Inceptisols
• C. Aridisols
• D. Gelisols

Hint:

Key Soil Order Mappings for Indian Soils:
- Black soils Regur $\rightarrow$ Vertisols (Montmorillonite clay, high shrink-swell).
- Alluvial soils $\rightarrow$ Inceptisols Entisols.
- Red soils $\rightarrow$ Alfisols.
- Laterite soils $\rightarrow$ Ultisols Oxisols.
- Desert soils $\rightarrow$ Aridisols.

Answer 1

The Correct Option is A

Concept:
The USDA Soil Taxonomy system classifies soils globally into 12 distinct soil orders based on diagnostic horizons, weathering degree, moisture regimes, and dominant mineralogy.
Black soils (commonly known in India as Regur soils or Black Cotton Soils) are extensively distributed across the Deccan basalt plateau (Maharashtra, Madhya Pradesh, Gujarat, Karnataka).
Their unique physical behavior and deep cracking characteristics place them within a specific taxonomic order.

Step 1: Identifying the Diagnostic Features of Black Soils:
Black cotton soils are clayey soils with a high proportion of expanding 2:1 lattice clay minerals (chiefly montmorillonite smectite group).
They exhibit high swelling when wet and severe shrinkage upon drying, forming wide, deep vertical cracks during dry seasons.
This swelling and shrinking causes a natural self-plowing and churning action (pedoturbation), leading to the development of micro-relief features called gilgai and polished shear planes called slickensides.

Step 2: Mapping to USDA Soil Orders:
- Vertisols: Soils characterized by high clay content ($>30\%$), deep cracking, high shrink-swell capacity, and slickensides. The prefix "Vert-" comes from the Latin verto (to turn or invert), reflecting this churning action. Thus, black soils belong to Vertisols.
- Inceptisols: Inception-stage soils with minimal horizon development.
- Aridisols: Desert soils of arid regions with low organic matter.
- Gelisols: Cold-climate permafrost soils.

Step 3: Final Answer:
Therefore, black soils belong to the order Vertisols, which is option (A).