Difference Between Organic and Inorganic Nitrogen

The key difference between organic and inorganic nitrogen is that the organic nitrogen is the nitrogen that occurs in organic compounds whereas the inorganic nitrogen is nitrogen that occurs in inorganic compounds.

Organic compounds are chemical species containing C and H atom as essential components. When these compounds contain nitrogen as well, this nitrogen is organic nitrogen. Inorganic compounds are chemical species that has chemical elements other than carbon and hydrogen. But there can be carbon and hydrogen in inorganic compounds as well. However, it is not essential to have these chemical elements as for organic compounds. Then the nitrogen atoms bound to these compounds are inorganic nitrogen. We use these terms mainly regarding soil chemistry.

1. Overview and Key Difference
2. What is Organic Nitrogen
3. What is Inorganic Nitrogen
4. Side by Side Comparison – Organic vs Inorganic Nitrogen in Tabular Form
5. Summary

What is Organic Nitrogen?

Organic nitrogen is the nitrogen atoms that occur in organic compounds. This form of nitrogen is common in soils. The organic matter in soil includes the residues of decomposing plant and animal matter and humus. These organic fractions contain nitrogen that incorporates into the organic matter during the soil development. Since the organic matter content in soil depends on the long-term moisture contents and temperature trends, the organic nitrogen content in the soil also varies. For example, due to the cultivation, the organic matter content of soil decreases due to increase oxidation of these organic compounds, which leads to reducing the soil organic matter nitrogen for crop uptake. Moreover, the organic nitrogen plays an important role in soil nitrogen cycling and crop production.

In general concept, the term organic nitrogen refers to any organic compound containing nitrogen. For example, amino acids, proteins, nucleotides, etc. In another approach, the term organic nitrogen refers to the nitrogen fraction in aquatic environments. We can divide this fraction into two groups as truly dissolved organic nitrogen and particulate organic nitrogen.

What is Inorganic Nitrogen?

Inorganic nitrogen is the nitrogen atoms that occur in inorganic compounds. Unlike organic compounds, inorganic compounds do not contain carbon and hydrogen as essential components. These compounds may or may not contain carbon and hydrogen, and there are many other chemical elements which make up inorganic compounds.

Figure 01: The Nitrogen Cycle shows the Inorganic Nitrogen in the Soil

In soil chemistry, we talk about inorganic nitrogen mainly in the nitrogen cycle. For example, ammonium (NH₄⁺) and nitrates (NO₃^–) predominate in the inorganic fraction of the soil. These are the major form that plants can uptake for their needs. In addition, ammonium occurs in both exchangeable and non-exchangeable forms. The other forms of inorganic nitrogen in soil are nitrogen gas (N₂) and nitrites (NO₂^–).

What is the Difference Between Organic and Inorganic Nitrogen?

Organic nitrogen is the nitrogen atoms that occur in organic compounds. The organic nitrogen includes amino acids, proteins, nucleotides, etc. along with nitrogen bound to residues of decomposing plant and animal matter and humus. Inorganic nitrogen is the nitrogen atoms that occur in inorganic compounds. This category mainly includes ammonium (NH₄⁺), nitrates (NO₃^–), nitrogen gas (N₂) and nitrites (NO₂^–).

Summary – Organic vs Inorganic Nitrogen

Both organic and inorganic nitrogen forms occur in the environment; soil, aquatic systems and air. The key difference between organic and inorganic nitrogen is that the organic nitrogen is the nitrogen that occurs in organic compounds whereas the inorganic nitrogen is nitrogen that occurs in inorganic compounds.

Reference:

1. “Soils – Part 5: Nitrogen as a Nutrient.” Plant and Soil Sciences ELibrary. Available here
2. “Nitrogen (Organic vs Inorganic) – Cold War Organics.” Cold War Organics. Available here