Question

Given below are two statements:
Statement (I): The sum of matric and osmotic potential is called 'hydraulic head' which is a useful index for characterizing the energy status of soil-water with respect to plant-water uptake.
Statement (II): Hydraulic potential is useful in evaluating the direction and intensity of water moving forces in the soil profile.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Recall that hydraulic head normally combines gravitational and matric potential, not matric and osmotic potential.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
This question checks how well you know the components that make up total soil water potential, and which of those components is actually called hydraulic head or hydraulic potential.

Step 2: Key Formula or Approach:
Total soil water potential is made up of several parts: gravitational potential (position in the soil profile), matric potential (attraction of water to soil particle surfaces and pores), pressure potential (in saturated soil), and osmotic or solute potential (from dissolved salts).
Hydraulic head, or hydraulic potential, in standard soil physics is defined as the sum of the gravitational potential and the matric or pressure potential, expressed as an equivalent height of water. It is this hydraulic head whose gradient drives water flow through the soil, following Darcy's law.

Step 3: Detailed Explanation:
Statement (I) claims that hydraulic head is the sum of matric and osmotic potential. This is incorrect on two counts. First, hydraulic head is properly the sum of gravitational and matric (or pressure) potential, not matric and osmotic. Second, osmotic potential barely affects bulk water movement through ordinary soil pores, it mainly matters where a semipermeable membrane is present, such as at plant root cell membranes, so lumping it into hydraulic head is a mistake. Statement (I) is therefore false.
Statement (II) is a standard, well accepted fact: because water always moves from a point of higher hydraulic potential to a point of lower hydraulic potential, mapping out hydraulic potential at different depths in a soil profile tells us both the direction water will move and how strong that driving force is. Statement (II) is true.
Since (I) is false and (II) is true, option 4 is correct, ruling out options 1, 2 and 3.

Step 4: Final Answer:
Statement (I) is incorrect (hydraulic head is gravitational plus matric potential, not matric plus osmotic), while Statement (II) is correct, so the answer is option 4.