Carbon/Nitrogen Ratio

Page reviewed:  15/06/2026

The carbon-to-nitrogen ratio (C/N) is important for the decomposability of organic material. At high ratios, approximately 25 and above, competition for nitrogen is strong, resulting in a reduced rate of decomposition and nitrogen deficiency for plants.

High C/N ratios are found, for example, in old, decaying sawdust piles and in mor humus layers.

About the carbon/nitrogen ratio

The C/N ratio varies between different soils and types of organic material. In certain types of fresh litter, such as bark flakes, the C/N ratio can be close to 100, but in well-decomposed organic matter it may be around 10.

In the mor layer of Swedish forest soils, the average C/N ratio is just over 30, but it decreases as the humus form becomes more nutrient-rich (moder, mull-like moder, and mull). In the humus form mull, the average C/N ratio is around 17 (Nilsson et al., 2015).

The maps presented below show the C/N ratio in the humus layer (O horizon), the eluviated horizon (E horizon), the illuvial horizon (B horizon), the BC horizon (45–55 cm below the soil surface), and the C horizon (55–65 cm below the humus layer), based on the sampling and measurements carried out during 1993–2002.

Horizon  

Total

Mor

Mull

Peat

Comparison

O

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B

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BC

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C

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Contact

  • Johan Stendahl, head of department and researcher
    Biogeochemistry of Forest Soils