Certified Crop Advisor Practice Exam

The maximum value for plant available water is?

1. the difference between field capacity and saturation

2. the difference between wilting point and field capacity

3. the average moisture content of surface soil

4. the total water in the soil

The correct answer is: the difference between wilting point and field capacity

The maximum value for plant available water is defined as the difference between the wilting point and field capacity. Field capacity refers to the amount of water held in the soil after excess water has drained away and the rate of downward movement has decreased. This represents the maximum water content that the soil can retain against the force of gravity, making it available for plant use. Wilting point is the minimal moisture level in the soil that plants can extract water. At this point, the water is held too tightly to the soil particles for plants to absorb it effectively, leading to wilting. The difference between these two measurements indicates the amount of water that plants can actually use—essentially, the range of moisture that is readily available for uptake by plant roots. Therefore, this answer correctly identifies the maximum value for plant available water, which is crucial for determining irrigation needs and managing soil health in agricultural practices. In contrast, the other choices focus on other aspects of soil moisture. The difference between field capacity and saturation does not provide a measure of water that is available to plants. The average moisture content of surface soil does not specifically indicate what is available for plant uptake, and the total water in the soil includes water that may not be accessible to plants due to saturation