What is Carbon to Nitrogen Ratio?


The carbon to nitrogen ratio is also represented in other forms, like C/N ratio, C:N, carbon-to-nitrogen ratio, etc. It can be used as a ratio of the mass of carbon to the mass of nitrogen in compost. A material, for example, having 30 times as much carbon as nitrogen is said to have a C:N ratio of 30:1, simply speaking, a C:N ratio of 30.

The Importance of Carbon to Nitrogen Ratio
The subject of the carbon/nitrogen ratio is an indispensible issue in composting. The decomposition of organic matter is affected by the presence of carbon and nitrogen. For microorganisms, carbon is a source of energy, and nitrogen is necessary for building cell structure. When the energy source, carbon, is less than that required for converting available nitrogen into protein, the excess nitrogen is lost as ammonia. This causes a waste of nitrogen. If there is too much carbon, decomposition slows when the nitrogen is used up.


To complete the nitrogen cycle and continue decomposition, the microbial cells will utilize any available soil nitrogen in the proper proportion to make use of available carbon. The soil nitrogen will be immobilized and will not be available as a fertilizer for growing plants until some later season when it is no longer being used in the life-cycles of soil bacteria.

Proper Ratio of Carbon to Nitrogen
When composting, if the carbon is completely consumed, microbial activity utilizes a C/N ratio of 30-35:1. However, this is often not the case. Practically, a compost should have an initial C/N ratio of 20-30:1, means that microorganisms that digest compost need about 30 parts of carbon for every part of nitrogen they consume.
Blend Greens and Browns Properly to Achieve the Ideal Carbon to Nitrogen Ratio
Desired C/N ratios can be achieved by blending common used substrates of known C/N content. We often call them browns and greens, while browns are a source of carbon and greens provide nitrogen.


Greens that we can use include green leaves, coffee grounds and filters, tea bags, raw fruit and vegetable scraps, human or animal hair, egg shells, grains, feathers, Blood meal (extremely rich in nitrogen), fresh green grass clippings and plant trimmings grown without pesticides or weed killers.
Browns include woodchips, cold wood ash from untreated wood, twigs and branches, sawdust from untreated wood, straw, corncobs and stalks, yard waste, shredded newspaper and tissue paper, dry leaves, dried grass clippings, small pieces paperboard, i.e., cereal boxes, paper plates and napkins.


Carbon to nitrogen ratio does not mean that you need a volume of brown materials that is thirty times greater than the amount of green matter. Nitrogen-rich materials still contain more carbon than nitrogen. So to get that 30:1 carbon-to-nitrogen ratio, you just need to combine one part nitrogen-rich materials with three parts carbon-rich materials. People have concluded typical ranges. Use them as a guide to figure proportions of browns and greens when you make a compost, but never emphasis too much on the precision measurements.