Certified Crop Advisor Practice Exam

Max ET generally occurs when:

1. soil moisture is abundant

2. temperature is lowest

3. atmospheric demand peaks

4. humidity is high

The correct answer is: atmospheric demand peaks

Max ET, or maximum evapotranspiration, typically occurs when atmospheric demand peaks. This is driven by factors such as increased temperature, wind speed, and low humidity, which together create conditions where moisture is rapidly drawn from soil and plants into the atmosphere. During periods of high atmospheric demand, the capacity of air to hold moisture increases, leading to a higher rate of evapotranspiration. Soil moisture is important but, in conditions of abundant moisture, the rate of ET may not reach its maximum because the limiting factor lies more in atmospheric conditions than in soil availability. Similarly, lower temperatures usually result in reduced rates of ET since cooler air holds less moisture and can lead to less evaporation from soils and transpiration from plants. High humidity creates a saturated atmosphere which reduces the capacity of the air to absorb additional moisture, thus not favoring higher rates of evapotranspiration.