Fertilizer grade notation “5–10–5”: In the standard N–P–K labeling system for fertilizers, what do the numbers 5–10–5 specifically indicate about nutrient analysis by mass percent?

Introduction / Context:
Bag labels such as 5–10–5, 10–26–26, or 20–20–0 follow a global convention for reporting fertilizer analysis. Understanding this convention ensures correct nutrient budgeting, pricing per unit nutrient, and proper field application rates across crops and soils.

Given Data / Assumptions:

• The sequence is nitrogen (N) – available phosphate (as P2O5) – soluble potash (as K2O).
• Values are weight percentages of the bag contents.
• “Available phosphate” and “soluble potash” are expressed as oxide-equivalents by long-standing industry convention.

Concept / Approach:
The first number is the mass percent of elemental nitrogen. The second and third are not elemental P or K but their oxide forms P2O5 and K2O as defined in fertilizer regulations. A 5–10–5 grade therefore guarantees at least 5% N, 10% P2O5, and 5% K2O by mass. The remainder of the product comprises other nutrients, conditioners, or carrier materials depending on formulation.

Step-by-Step Solution:

Verification / Alternative check:
Regulatory definitions and fertilizer standards worldwide (e.g., AOAC/FAO) align with the oxide-equivalent convention, ensuring consistent marketplace labeling.

Why Other Options Are Wrong:

• “5–10% active nutrients overall”: misreads the notation; each number is a specific nutrient percentage.
• “None of these”: incorrect because option (a) is correct.
• “N2 as a gas”: nitrogen is not reported as molecular nitrogen; the analysis is based on total N content.

Common Pitfalls:
Confusing P2O5 and K2O with elemental P and K; conversion factors are needed if elemental values are required for scientific calculations.

Final Answer:
5% N, 10% P2O5, and 5% K2O.