Certified Landscape Irrigation Auditor

What is meant by permanent wilting point?

1. The water available for plant uptake

2. The soil moisture level where plants can no longer extract water

3. The ideal moisture content for healthy plants

4. The maximum water holding capacity of soil

The correct answer is: The soil moisture level where plants can no longer extract water

The concept of permanent wilting point refers to the specific moisture level in the soil at which plants can no longer extract sufficient water to meet their physiological needs, resulting in irreversible wilting. At this point, the water available has decreased to a level where the moisture potential in the soil is so low that the roots cannot absorb water, leading to stress in plants. Understanding this point is essential for irrigation management, as it helps in determining when to irrigate. If soil moisture drops below this level, plants suffer from water stress, which can hinder their growth, reduce productivity, and potentially lead to death. The other choices highlight related concepts but do not define permanent wilting point accurately. For instance, the available water for plant uptake refers to moisture levels above the permanent wilting point and field capacity, while the ideal moisture content and maximum water holding capacity pertain to different aspects of soil moisture management.