Certified Landscape Irrigation Auditor

What is reference ET?

1. The amount of water required by drought-resistant plants

2. The amount of water a plant will use when water and nutrients are not limited

3. The total water available in the soil

4. The estimated evaporation from open water bodies

The correct answer is: The amount of water a plant will use when water and nutrients are not limited

Reference ET, or reference evapotranspiration, represents the amount of water a plant would use under optimal conditions, where water and nutrients are not limited, and other growth factors such as light and temperature are ideal. It serves as a standard measurement to assess evaporation and transpiration rates for different types of plants, typically grass, as a baseline for irrigation needs. This measurement is vital for landscape irrigation as it helps in determining how much water should be applied to maintain healthy plant growth without over- or under-watering. Understanding reference ET allows irrigation managers to make more informed decisions on scheduling irrigation and managing water resources effectively. Other options highlight different aspects of water usage or availability but do not accurately define reference ET. For example, the reference to drought-resistant plants focuses on a specific plant type rather than a baseline measurement, while the total water in the soil pertains to soil moisture rather than plant water use under optimal conditions. Similarly, evaporation from open water bodies describes a separate phenomenon related to water loss in an environmental context.