Question

For a commercial fertilizer designated as 5-20-20 the numbers indicate what information about the composition?

• A. 5% K, 20% N, 20% P
• B. 5% N, 20% Na, 20% S
• C. 5% N, 20% P$_2$O$_5$, 20% K$_2$O
• D. 5% K$_2$O, 20% N, 20% P$_2$O$_5$

Hint:

Remember: In N-P-K fertilizer labels, values refer to N, P$_2$O$_5$, and K$_2$O respectively — not the elemental forms of P and K.

Answer 1

The Correct Option is C

Fertilizer labels typically follow the format: N-P-K, where:
- The first number represents the percentage of Nitrogen (N)
- The second number indicates the percentage of phosphorus in the form of phosphate ($\text{P}_2\text{O}_5$)
- The third number denotes the percentage of potassium in the form of potash ($\text{K}_2\text{O}$)
Thus, a fertilizer labeled as 5-20-20 contains:
- 5% Nitrogen (N)
- 20% Phosphate ($\text{P}_2\text{O}_5$)
- 20% Potash ($\text{K}_2\text{O}$)
This standardized system helps farmers quickly understand the nutrient content and make decisions based on soil requirements and crop needs.
Let’s quickly dismiss the incorrect options:
- Option 1: Wrong order and incorrect elements (K listed first, P given as elemental P)
- Option 2: Incorrect elements — Na and S are not standard primary nutrients in this format
- Option 4: Wrong order — K$_2$O listed first, contradicting standard N-P-K order
Thus, the correct answer is:
5% N, 20% P$_2$O$_5$, 20% K$_2$O