Certified Crop Advisor Practice Exam

The maximum plant available water is calculated as:

1. field capacity + wilting point

2. field capacity - wilting point

3. wilting point / field capacity

4. field capacity x wilting point

The correct answer is: field capacity - wilting point

The maximum plant available water is calculated as the difference between field capacity and the wilting point. Field capacity is the amount of water that soil can hold after excess water has drained away and the rate of downward movement has decreased. It represents the maximum amount of water the soil can retain for plant use. The wilting point is the minimum soil moisture level at which plants can no longer extract water; when the available water drops below this level, plants will start to wilt due to moisture deficiency. By subtracting the wilting point from field capacity, you obtain the amount of water that is actually available to plants for uptake. This value is crucial for understanding soil water dynamics and managing irrigation effectively, as it informs how much water the soil can supply to plants before they begin to experience stress. The other options do not accurately reflect the relationship needed for calculating plant available water. For instance, adding field capacity and wilting point does not yield a meaningful metric in this context, and using division or multiplication in the formula detracts from the simple difference that defines available water.