Soil-plant-water relation: The condition at which plants can no longer extract sufficient moisture from the soil for their needs is called the ________.

Introduction / Context:
Irrigation engineering and agronomy use specific moisture benchmarks to schedule irrigation. Two key points are field capacity (upper limit of easily available water) and permanent wilting point (lower limit where plants cannot recover turgidity).

Given Data / Assumptions:

• Unsaturated soil supporting crops.
• Moisture extraction occurs from capillary water held at various suctions.
• Plant stress increases as soil matric potential becomes more negative.

Concept / Approach:
Permanent wilting point is the soil water content at which plants, even after being placed in a humid chamber, do not regain turgidity. Below this, remaining water is bound too strongly to soil particles to be usefully extracted by roots.

Step-by-Step Solution:
Identify the moisture state where extraction by plants effectively ceases.At field capacity, extraction is easy; as soil dries, availability reduces.At the permanent wilting point, plants fail to extract sufficient water and wilt irreversibly.

Verification / Alternative check:
Standard soil-water characteristic curves show available water range between field capacity and permanent wilting point; irrigation scheduling targets depletion fractions that avoid reaching PWP.

Why Other Options Are Wrong:

• Maximum saturation point: Refers to full saturation, opposite situation.
• Ultimate utilisation point: Non-standard term.
• Field capacity: Upper benchmark, not wilting condition.
• None of these: Incorrect because PWP is the accepted term.

Common Pitfalls:
Confusing “temporary wilting” (reversible overnight) with permanent wilting; misusing field capacity as a stress limit.

Final Answer:
Permanent wilting point