Question

According to Mohr and van Baren, arrange the following five stages of soil development
(A) Juvenile Stage
(B) Senile
(C) Un-weathered parent material stage
(D) Virile
Choose the correct answer from the options given below:

• A. (A), (B), (C), (D).
• B. (C), (A), (D), (B).
• C. (B), (A), (D), (C).
• D. (C), (B), (D), (A).

Hint:

Chronology of Mohr and van Baren's soil development stages:
Initial (Un-weathered) $\rightarrow$ Juvenile $\rightarrow$ Virile (Peak fertility) $\rightarrow$ Senile (Depleted) $\rightarrow$ Final.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Soil development (pedogenesis) is a continuous, long-term geological and biochemical process in which parent rock and minerals are converted into mature soil profiles.
To describe the progressive weathering and developmental stages of tropical soils, researchers Mohr and van Baren (1954) proposed a classification consisting of five distinct stages.
These stages describe the soil's life cycle from fresh, un-weathered mineral material to highly weathered, nutrient-depleted, and inactive residues.

Step 2: Detailed Explanation:
Let us review the five stages of soil development proposed by Mohr and van Baren in chronological order:
1. Initial Stage (Un-weathered parent material stage - C):
This represents the starting point of soil formation.
The parent material (rock or sediment) is virtually un-weathered, and no soil profile development or distinct horizons have occurred.
2. Juvenile Stage (A):
Weathering of the parent material has initiated.
Easily weatherable minerals begin to break down, releasing basic cations.
The soil profile is thin, but early horizonation begins to appear.
3. Virile Stage (D):
This is the stage of active weathering and maximum fertility/productivity.
Clay minerals (such as smectites or illites) are formed, and the soil possesses a high cation exchange capacity (CEC) and abundant nutrient availability.
A well-developed, mature soil profile is established.
4. Senile Stage (B):
Weathering is highly advanced.
Most primary minerals have decomposed, and highly soluble nutrients have been leached out of the profile.
The soil is dominated by highly resistant minerals like kaolinite, gibbsite, and iron/aluminum oxides, leading to a decline in soil fertility and CEC.
5. Final Stage:
The soil development is complete, and the soil is virtually inactive, consisting only of highly weathered, chemically inert mineral residues.
Tracing this chronological sequence gives: (C) Un-weathered parent material \(\rightarrow\) (A) Juvenile Stage \(\rightarrow\) (D) Virile \(\rightarrow\) (B) Senile.
This matches the sequence: (C), (A), (D), (B), corresponding to option (B).

Step 3: Final Answer:
Therefore, the correct chronological sequence of the soil development stages is (C), (A), (D), (B).