Question

Given below are two statements:

Statement (I): The gravitational potential is independent on the relative elevation and is dependent on chemical and pressure conditions of soil water.

Statement (II): Osmotic potential can be defined as the amount of work that a unit quantity of water in an equilibrium soil water system is capable of doing when it moves to another equilibrium system identical in all respects except that there are no solutes.

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:

Ask what each type of soil water potential is physically caused by before judging the statements.

Answer 1

The Correct Option is D

A quick way to check these two statements is to ask what each potential component actually responds to.

Gravitational potential, often written $\psi_g = \rho_w g z$, changes only with $z$, the height of the water above or below a reference plane. Nothing in this expression involves salt content or pressure, so a soil water potential that depends on chemical and pressure conditions while ignoring elevation cannot be the gravitational term. Statement (I) has the dependency backwards, so it fails.

Osmotic potential is defined through a thought experiment: take the soil water and imagine transporting it, at the same height and same gas pressure, into a parallel system where the solutes have been removed. The work this movement takes is the osmotic potential. Statement (II) restates this definition almost word for word, so it stands as true.

Putting the two results together, only the second statement survives.

\[\boxed{\text{Statement (I) false, Statement (II) true}}\]