Certified Crop Advisor Practice Exam

This substance is critical for plant nutrient uptake and is most available at pH levels around 6.8.

1. Potassium

2. Calcium

3. Phosphorus

4. Molybdenum

The correct answer is: Phosphorus

The correct choice highlights phosphorus as a substance that is crucial for plant nutrient uptake and is most available at a pH level of around 6.8. Phosphorus plays a vital role in energy transfer within plants, being a key component of ATP (adenosine triphosphate), the molecule that stores and transfers energy in cells. It is also essential for photosynthesis and the formation of nucleic acids, which are critical for plant growth and reproduction. Optimal pH levels significantly influence the availability of phosphorus in the soil. At a pH of around 6.8, phosphorus becomes more soluble and accessible to plants. When the soil's pH dips below this level, phosphorus can bind with iron and aluminum, making it less available for uptake. Conversely, at higher pH levels, phosphorus can interact with calcium, forming insoluble compounds. Therefore, maintaining a soil pH around 6.8 is beneficial for phosphorus availability, ultimately supporting healthy plant growth.