Certified Crop Advisor Practice Exam

If a soil contains 100 lb/P/acre, it contains _______ ppm P?

1. 25

2. 50

3. 75

4. 100

The correct answer is: 50

To determine how many parts per million (ppm) of phosphorus (P) are present when a soil contains 100 pounds of P per acre, it's important to understand the conversion between these measurements. One acre of soil weighs approximately 2 million pounds (this can vary based on soil depth and soil type, but 2 million pounds is a common approximation for calculations). To convert pounds per acre to parts per million (ppm), you can use the formula: \[ \text{ppm} = \left( \frac{\text{pounds per acre}}{\text{total weight of soil in pounds per acre}} \right) \times 10^6 \] By substituting the values: \[ \text{ppm} = \left( \frac{100 \text{ lb P/acre}}{2,000,000 \text{ lb/acre}} \right) \times 10^6 \] When you perform the calculation: \[ \text{ppm} = \left( \frac{100}{2,000,000} \right) \times 10^6 = 50 \text{ ppm} \] Thus, if a soil contains 100 lb of phosphorus per