Relationship between Nitrate Nitrogen (NO₃-N), Ammonium Nitrogen (NH₄-N), and Total Nitrogen (TN)

1. Definition

• NH₄-N (Ammonium Nitrogen): Inorganic nitrogen present in the form of ammonium ions.

• NO₃-N (Nitrate Nitrogen): Inorganic nitrogen present in the form of nitrate ions.

• TN (Total Nitrogen): The sum of all nitrogen species in a sample, including organic nitrogen, ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen.

2. Quantitative Relationship

TN=Organic N+NH4​−N+NO2​−N+NO3​−N

In most environmental and water quality conditions:

• NO2​−N (nitrite nitrogen) is usually very low and can be neglected.

• Therefore:

  TN≈Organic N+NH4​−N+NO3​−N

This means:

TN>NH4​−N+NO3​−N

Only when organic nitrogen and nitrite nitrogen are negligible can the approximation hold:

TN≈NH4​−N+NO3​−N

3. Transformation Relationship (Nitrogen Cycle)

1. Organic nitrogen → (Ammonification) → NH₄-N

2. NH₄-N → (Nitrification under aerobic conditions) → NO₂-N → NO₃-N

3. NO₃-N → (Denitrification under anoxic conditions) → N₂ (released to atmosphere)

NH₄-N and NO₃-N are key intermediate inorganic forms in the nitrogen cycle, while TN represents the total nitrogen pool.