Question

Soil Water Content increasing order
(A) field capacity
(B) Oven dry
(C) Hygroscopic
(D) Permanent wilting
Choose the correct answer from the options given below :

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

Hint:

Soil water tension (bars) is inversely proportional to soil water content. High tension (31 bars, Hygroscopic) = low water content. Low tension (0.33 bars, Field Capacity) = high water content. Oven dry is the absolute zero baseline.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Soil water is held in soil pores at varying degrees of tension (suction).
As the soil dries, the remaining water is held in smaller pores at higher tension, resulting in lower total soil water content.

Step 3: Detailed Explanation:
Let us analyze the soil water content at different physical limits and arrange them in increasing order:
- (B) Oven dry: At this state, the soil is dried in an oven at $105^\circ\text{C}$ until it reaches a constant weight. All free, capillary, and hygroscopic water is removed, leaving a water content of 0%.
- (C) Hygroscopic coefficient: This represents the water held tightly as a thin molecular film on soil solid surfaces at very high tension (typically between 31 to 10,000 bars). This water is non-liquid and unavailable to plants.
- (D) Permanent wilting point (PWP): This is the soil moisture limit below which plants can no longer extract water and wilt irreversibly. It is held at a tension of 15 bars.
- (A) Field capacity: This is the water content retained in the soil after excess gravitational water has drained away, typically 2-3 days after a heavy rain or irrigation. It is held at a very low tension of 0.1 to 0.33 bars, representing a highly moist state.
Arranging these states in increasing order of actual water content:
\[ \text{Oven dry (B)} < \text{Hygroscopic (C)} < \text{Permanent wilting (D)} < \text{Field capacity (A)} \]
This corresponds to the sequence: (B), (C), (D), (A).
This matches Option (B).

Step 4: Final Answer:
The correct increasing order of soil water content is (B), (C), (D), (A).