Certified Landscape Irrigation Auditor

What defines available water?

1. The total water in the soil

2. The water stored between field capacity and permanent wilting point

3. The water available from irrigation systems

4. The water content required for seed germination

The correct answer is: The water stored between field capacity and permanent wilting point

Available water is defined as the amount of water that can be readily absorbed by plant roots, which is specifically the water stored in the soil between field capacity and permanent wilting point. Field capacity refers to the amount of water soil can hold after excess water has drained away and the rate of downward movement has decreased, representing the maximum amount of water the soil can hold against the force of gravity. On the other hand, the permanent wilting point is the minimal soil moisture level at which plants can no longer extract water, leading to wilting and potential death if the moisture is not replenished. Therefore, the difference between these two points represents the range of soil moisture that is accessible for plant use—this is where the majority of plant uptake occurs. Recognizing this definition is crucial for understanding irrigation practices and soil management to ensure plants have adequate water for optimal growth. In contrast, the other choices do not accurately represent the concept of available water. The total water in the soil encompasses all forms of moisture, not just what is available for plant uptake. The water from irrigation systems refers to artificially supplied water, which is separate from the water that plants can utilize based on soil characteristics. Lastly, while the water content required for seed germination is important