Nitrogen fertiliser valuation: The “fertiliser value” of a nitrogenous product is expressed in terms of its percentage of which chemical quantity?

Introduction / Context:
Nitrogen fertilisers are purchased and applied on the basis of how much nitrogen they supply to crops. Labels therefore report the percentage of elemental nitrogen, irrespective of whether the product is urea, ammonium nitrate, ammonium sulphate, or other forms. This question clarifies that “fertiliser value” for nitrogen means % N, not % N2, NO2−, or HNO3.

Given Data / Assumptions:

• Standard agronomic labeling is assumed.
• Products release plant-available nitrogen in ammonium or nitrate form after soil processes.
• We seek the unit used on the label, not the chemical pathway in soil.

Concept / Approach:
Fertiliser value for N is expressed as mass percent of elemental nitrogen, % N. For example, urea is ~46% N, ammonium nitrate ~33–35% N, ammonium sulphate ~21% N. The gas N2 is not applied directly to soil, nitrite is an intermediate and rarely present in fertilisers, and nitric acid is a manufacturing reagent rather than the delivered nutrient basis.

Step-by-Step Solution:

Verification / Alternative check:
National fertiliser control orders and international standards specify nitrogen content as % N on a mass basis for product certification and trade.

Why Other Options Are Wrong:

• N2: atmospheric gas, not the label basis.
• NO2− and HNO3: not used for value expression.
• NH4NO3 equivalent: not a universal unit for nitrogenous products.

Common Pitfalls:
Confusing oxide-equivalent labeling used for P and K with the direct elemental % labeling used for N.

Final Answer:
Elemental nitrogen (N) content