What is a Carbon to Nitrogen Ratio (C:N)?
Photo Credit: https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/ nrcseprd341633.pdf
The carbon-to-nitrogen ratio in soil is the ratio of the mass of carbon-to-nitrogen. A C:N ratio of 10:1 means there are ten units of carbon (C) for each unit of nitrogen (N) in the soil. This ratio can have a significant impact on how the soil functions; i.e. crop residue decomposition, particularly residue-cover on the soil and crop nutrient cycling (predominantly N).
It is important to understand the C:N ratio when planning cash crops rotations and cover crops in rotations. Soils with a carbon-to-nitrogen (C:N) ratio of 24:1 have the optimum ratio for soil microbes to stimulate release of nutrients like N, phosphorous and zinc to crops. This ratio influences the amount of soil-protecting residue cover that remains on the soil. It is important to understand these ratios when planning cash crops rotations and cover crops in rotations. For crops and cover crops with a low C:N ratio (hairy vetch, 11:1) the quicker microbes consume residue, the less time soil is covered. On the other hand, for crops with a high C:N ratio (cereal rye, 80:1) microbes have to find additional N to balance out the excess C as they consume the cereal rye. This could temporarily create an N deficit (immobilization). Additional N may have to be supplemented for crops that have a high nitrogen requirement to prevent a yield drag, such as corn.
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| Title | Source | Resource type and Date | Short Summary / Preview |
|---|---|---|---|
| Carbon to Nitrogen Ratios in Cropping Systems | USDA – NRCS | Fact sheet
Jan 2011 |
Carbon to Nitrogen ratio (C:N) is a ratio of the mass of carbon to the mass of nitrogen in a substance. Since the C:N ratio of everything in and on the soil can have a significant effect on crop residue decomposition, particularly residue cover on the soil and crop nutrient cycling (predominantly nitrogen), it is important to understand these ratios when planning crop rotations and the use of cover crops in agricultural systems. |
| Compost Production and Use | Michigan State University | Fact sheet
2013 |
Composting manure can provide the desired C:N ratio for soil health. |
| A Strategy to Improve Soil Health in a Midwest Corn-Soybean Cropping System | Conservation Cropping Systems Initiative, USDA-NRCS | Fact sheet
Jan 2014 |
Farmers who use quality no-till systems to improve soil health find that the integration of single cropping practices into a system provide benefits to the whole system that exceed the sum of the parts. |
| Title | Source | Resource type and Date | Short Summary |
|---|---|---|---|
| C/N Ratio | Cornell University | Webpage
1996 |
C:N ratio, importance for composting. How to calculate. |
| MCSE: Soil C and N | Michigan State University, LTER | Extension/Research Protocol
not dated |
Protocol to measure soil C and N. |
Technical review: March 31, 2020