Question

Prismatic soil structure is a distinct feature in

• A. Red soils
• B. Black soils
• C. Alluvial soils
• D. Sodic soils

Hint:

Think about which problem soil has high exchangeable sodium that hardens into vertical columns.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks which soil type shows prismatic structure as its typical, identifying feature.

Step 2: Key Formula or Approach:
Soil structure describes how sand, silt and clay particles group into peds. Prismatic and columnar peds are vertical, column like blocks with flat or rounded tops that form when clay particles swell and shrink strongly and when sodium ions push particles apart.

Step 3: Detailed Explanation:
Sodic soils carry a high amount of exchangeable sodium on the clay surface. This sodium disperses the clay when the soil gets wet, and on drying the soil sets into hard, vertical columns, which is the prismatic or columnar structure used to identify these soils in the field.
Red soils are usually loose and porous with a crumb or granular structure because of good drainage and lower clay activity.
Black soils (regur soils) have high clay content and swell and shrink a lot, giving them a blocky or angular blocky structure with deep cracks in the dry season, not a prismatic one.
Alluvial soils are young, layered soils laid down by rivers and mostly show a single grain or weak granular structure.

Step 4: Final Answer:
Prismatic structure is the hallmark of sodic soils, so option 4 is correct.