Question

The soil hydraulic head is expressed by
(A). Potential energy per unit mass of soil water.
(B). Potential energy per unit volume of soil water.
(C). Potential energy per unit weight of soil water.
(D). Height of standing water on the soil surface.
Choose the correct answer from the options given below:

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

Hint:

Remember: - Energy per unit weight = Length dimensions (meters/centimeters head) - Energy per unit volume = Pressure dimensions (Pascalbar) - Energy per unit mass = Chemical potential ($\text{J/kg}$)

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Soil water potential represents the energy state of soil water relative to pure free water at a standard reference elevation.
It can be expressed in three different ways: per unit mass, per unit volume, or per unit weight.

Step 2: Detailed Explanation:
- Potential energy per unit mass ($\text{J/kg}$) is often represented by $\mu$.
- Potential energy per unit volume ($\text{J/m}^3$ or $\text{N/m}^2$, which is Pascal) is represented by pressure $P$.
- Potential energy per unit weight is expressed as equivalent water column height:
\[ \text{Head } H = \frac{\text{Energy}}{\text{Weight}} = \frac{mgh}{mg} = h \text{ (meters or centimeters)} \] By definition, "hydraulic head" is the soil water potential expressed strictly as potential energy per unit weight of soil water.

Step 3: Final Answer:
The soil hydraulic head is expressed only by potential energy per unit weight.