Certified Professional Horticulturist (CPH) Practice Exam

Which of the following factors most commonly contributes to nutrient lockout in plants?

1. Excessive soil acidity

2. Low temperatures

3. Frequent watering

4. High humidity

The correct answer is: Excessive soil acidity

Nutrient lockout in plants typically occurs when the pH of the soil is out of an optimal range for nutrient availability. Excessive soil acidity, which is characterized by a low pH, can lead to a situation where essential nutrients become less soluble and, therefore, less available for plant uptake. In acidic soils, certain nutrients like phosphorus and calcium may precipitate out of solution or become bound to soil particles, making them inaccessible to plants. While low temperatures, frequent watering, and high humidity can affect plant health in various ways, they are not as commonly linked to nutrient lockout as soil pH. Low temperatures can slow down metabolic processes but do not directly cause nutrient deficiencies. Frequent watering can lead to leaching of nutrients but is not equivalent to nutrient lockout. Furthermore, high humidity can impact transpiration and nutrient uptake indirectly but does not directly alter nutrient availability in the soil. Understanding the importance of pH in relation to nutrient availability is crucial for maintaining optimal growth conditions for plants.