The C/N ratio or carbon-to-nitrogen ratio is a ratio of the mass of carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 to the mass of nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 in a substance. It can, amongst other things, be used in analysing sediment

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

s and compost

Compost

Compost is organic matter that has been decomposed and recycled as a fertilizer and soil amendment. Compost is a key ingredient in organic farming. At its most essential, the process of composting requires simply piling up waste outdoors and waiting for the materials to break down from anywhere...

. Carbon-to-nitrogen ratios are an indicator for nitrogen limitation of plants and other organisms.

C/N ratios in the range 6-8:1 are usually from marine sources, whereas higher ratios are likely to come from a terrestrial source. (Dahlhem 1988).

For agricultural

Agriculture

Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...

 purposes, a compost should have a C/N ratio of 20-30:1.

An example of a device that can be used to measure this ratio is the CHN analyzer

CHN analyzer

A CHN Analyzer is a scientific instrument which can determine the elemental composition of a sample. The name derives from the three primary elements measured by the device: carbon , hydrogen and nitrogen...

.