Step 1: Understanding the Concept:
Soil structure is described using three parameters: type (shape), class (size), and grade (degree of distinctness).
The grade of soil structure refers to the strength and stability of the peds, representing how easily they maintain their shape when handled.
Grades of soil structure are assigned standardized numerical ratings from 0 to 3. Step 2: Detailed Explanation:
The standard ratings for the grades of soil structure are defined as follows:
- Grade 0 (Structureless): No observable aggregation or structural arrangement.
The soil is either single-grain (like sand) or massive (like a dense clay block). Thus, (A) matches (III).
- Grade 1 (Weak): Poorly formed, indistinct peds that break easily into a mixture of some whole peds and much unaggregated material when handled. Thus, (C) matches (IV).
- Grade 2 (Moderate): Well-formed, distinct peds that are moderately durable.
When handled, the soil breaks down into a mixture of mostly whole peds and little unaggregated material. Thus, (B) matches (I).
- Grade 3 (Strong): Highly durable, distinct peds that are clearly visible in the undisturbed soil profile.
They resist displacement and remain intact when the soil is handled. Thus, (D) matches (II).
Combining these pairs gives: (A) - (III), (B) - (I), (C) - (IV), (D) - (II).
This matches Option (D). Step 3: Final Answer:
The correct matching sequence is (A) - (III), (B) - (I), (C) - (IV), (D) - (II).
