YielixCompost Carbon and Nitrogen Balance
Build a recipe from masses, not ingredient labels
A compost recipe is made from wet, variable materials. The useful question is how much carbon and nitrogen each actual ingredient contributes after water is removed, not whether a material name has one universal C:N number.
Use the Compost C:N Ratio Calculator to revise measured wet mass, moisture, dry-basis carbon and dry-basis nitrogen for each ingredient.
Correct every ingredient to dry mass first
Enter moisture as a percentage of wet mass, and carbon and nitrogen as percentages of dry mass. Use kg throughout a metric recipe or lb throughout an imperial recipe; the result is unitless only because the same mass unit is used throughout.
Formula and units
dry mass = wet mass × (1 − moisture / 100) [kg or lb dry matter]
carbon mass = dry mass × dry carbon / 100 [kg or lb C]
nitrogen mass = dry mass × dry nitrogen / 100 [kg or lb N]
mixture C:N = Σ carbon mass ÷ Σ nitrogen mass [mass C : mass N]
mixture moisture = 100 × Σ water mass ÷ Σ wet mass [% wet basis]
Positive total wet mass and nitrogen are required; otherwise a finite C:N must not be displayed.
Worked example: why averaging ratios fails
Use the retained Metric fixture: A = 10 kg wet mass, 0% moisture, 50% dry carbon, 1% dry nitrogen; B = 10 kg, 0% moisture, 40% dry carbon, 4% dry nitrogen.
- Both are 10 kg dry mass.
- A contributes
5 kg Cand0.1 kg N; B contributes4 kg Cand0.4 kg N. - Totals are
9 kg Cand0.5 kg N. 9 ÷ 0.5 = 18: the result is 18:1, not the arithmetic average 30:1.
Change only A to 50% moisture: it has 5 kg dry mass, the mixture becomes 14.444:1, and 5 kg water in 20 kg wet mixture is 25% moisture.
Enter measured or deliberately assumed ingredient values, then inspect every dry-mass contribution
Compost Carbon-to-Nitrogen Ratio Calculator
Calculate a wet-mass-corrected compost mixture C:N ratio, moisture and each ingredient’s dry carbon and nitrogen contributions.
Use a starting goal as context, not a guarantee
Cornell describes approximately 30:1 as a starting compost context. It is not a universal target, maturity, temperature, odor, pathogen or nutrient-availability prediction.
Recipe creation is separate from field use: the Compost Application Rate Calculator uses finished-compost and crop assumptions, while SOM Build Plan explores longer-horizon carbon assumptions.
Assumptions and limitations
- Each analysis represents the material being mixed, the mixture is sufficiently uniform, and one mass unit is used across rows.
- The calculation does not model decomposition rate, loss, temperature, oxygen, mixing quality, pathogens, pH, salinity, nutrient availability, regulations or field response.
Common mistakes
- Averaging ingredient ratios: sum corrected carbon and nitrogen masses before dividing.
- Mixing wet- and dry-basis inputs: enter moisture separately.
- Treating a preset as a measurement: retain sources and replace assumptions with representative analyses.
- Turning recipe C:N into an application rate: finished-compost analysis and crop needs are separate inputs.
Sources
- Cornell Composting, Compost Chemistry — compost-condition context beyond this mass balance.