Practice Problems for Fertilizer Analysis
Agronomy 354

Remember:

a) A fertilizer contains nutrients plus other elements (often called carriers). The percentage nutrient can be calculated by knowing the weight of nutrient in the weight of fertilizer. This value is taken times 100 to get a percentage nutrient contained..
b) Regardless of the form of nutrient in fertilizer, the P is often expressed as P2O5 and the K as K2O (oxide basis).
c) A fertilizer analysis is expressed as N-P2O5-K2O where the nutrients are expressed as percentages.
d) The percentage of nutrient in a fertilizer = (lbs nutrient/lbs fertilizer) X 100.
e) The lbs of nutrients = lbs of fertilizer times % nutrient (decimal equivalent).
f) To determine the lbs of fertilizer needed = lbs nutrient divided by % nutrient (decimal equivalent).
g) If N+P2O5+K2O is indicated, this means lbs of nutrients and not percentages.

1. What is the fertilizer analysis of pure NH4NO3? (at wts: N=14, H=1, O=16)

2. If 120 lbs of NH4NO3 were applied per acre, how many lbs of N are applied?

3. If 160 lbs of starter (6-10-8) were applied per acre, how many lbs of N, P2O5, and K2O are applied?

4. If a soil test report calls for 80 lbs of K2O per acre, how many lbs of muriate of potash (KCl) must be applied to meet this requirement?

5. Some fertilizers are "dual labeled" in that they have both elemental and oxide form on the label. Also, most scientific literature reports all nutrient analyses on the elemental basis. If a bag of fertilizer were labeled as containing 40% K2O, what is the analysis when expressed as %K?

6. In a similar problem, assume the bag is labeled as 20% P. Calculate the percentage P2O5 in the bag.

7. If a 50-lb bag of urea (45-0-0) costs \$8.00, what is the cost per lb of N?

8. If P2O5 is worth 38¢ per lb and a ton of pure K2HPO4 sells for \$484, how much are you paying per lb of K2O? Hint: must determine the pounds of P2O5 and K2O (convert both to oxide basis) per 2000 pounds of K2HPO4.

9. Assume that you wish to make a bulk blend and add 300 lbs of 0-46-0 and 200 lbs of 0-0-60. What is the analysis of this blend (assume everything is on the oxide basis)?

10. A soil test report calls for 80 lbs P2O5 and 95 lbs K2O per acre. You have 20 acres that need fertilized. If the source of P2O5 is 0-46-0 and the source of K2O is 0-0-60, how many pounds of each fertilizer must you blend together to fill the truck going to the field? What will be the final analysis of the blended fertilizer?