Certified Crop Advisor Practice Exam

How many pounds of 10-20-10 fertilizer should be applied per acre if the recommendation is for 60 pounds of P205?

1. 150

2. 300

3. 450

4. 600

The correct answer is: 300

To determine how many pounds of 10-20-10 fertilizer are needed to supply 60 pounds of P2O5 (phosphorus pentoxide) per acre, understanding the nutrient composition of the fertilizer is essential. The numbers in the fertilizer formulation (10-20-10) represent the percentage by weight of nitrogen, phosphorus (as P2O5), and potassium (as K2O), respectively. In this case, 20% of the fertilizer's weight is phosphorus as P2O5. To find out how much fertilizer is required to provide 60 pounds of P2O5: 1. Calculate the amount of total fertilizer needed by using the percentage of phosphorus. 2. Since 20% of the fertilizer is P2O5, the following equation can be set up: Total fertilizer needed (in pounds) = Desired amount of P2O5 / Fraction of P2O5 in the fertilizer formulation Substituting the values: Total fertilizer needed = 60 pounds / 0.20 = 300 pounds This calculation reveals that 300 pounds of 10-20-10 fertilizer will deliver the required amount of phosphorus pentoxide (P2O5) for the application.