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Calcimator

Active Carbon Calculator

Permanganate-oxidizable carbon (POXC) from soil sample absorbance readings using the Weil et al. method.

Inputs

Results

POXC (mg C/kg soil)

540

KMnO4 consumed (%)37.5%
Active C fraction (%)3.5%
Soil health score (0-100)45
RatingModerate
How to Use This Calculator
  1. Enter your soil active carbon measurement from a permanganate oxidizable carbon (POXC) test in mg/kg.
  2. Input your soil texture class (sand, loam, clay) to set the reference baseline.
  3. Set your land use type (cropland, pasture, forest).
  4. Review the Active Carbon Score and the Biological Activity Rating.
  5. Use the Management Recommendations output to prioritize cover crops or compost additions.

How the result changes with Blank absorbance (550 nm)

Blank absorbance (550 nm)POXC (mg C/kg soil)
0.110
0.36631
0.65999
0.91,120.4

What each input means

Sample absorbance (550 nm)
Absorbance of diluted sample at 550 nm after KMnO4 reaction.
Blank absorbance (550 nm)
Absorbance of the unreacted KMnO4 blank solution at 550 nm.
Soil weight (g)
Dry weight of soil used in the assay (standard: 2.5 g).
KMnO4 solution volume (mL)
Volume of 0.02 M KMnO4 added to the soil (standard: 20 mL).

What each result means

POXC (mg C/kg soil)
Permanganate-oxidizable carbon — the labile, biologically active carbon pool.
KMnO4 consumed (%)
Percentage of permanganate oxidized by soil carbon.
Active C fraction (%)
Estimated active carbon as a share of total organic carbon.
Soil health score (0-100)
Normalized score based on typical POXC ranges (0-1200 mg/kg).

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Sample absorbance (550 nm) = 0.2, Blank absorbance (550 nm) = 0.32, Soil weight (g) = 2.5, KMnO4 solution volume (mL) = 20 = 4 input(s) provided
  2. Calculate POXC
    POXC = (molesReacted * mgCperMol) / soilWeightKg
    540 = 540
  3. Calculate KMnO4 consumed
    KMnO4 consumed = 1 - absSample / absBlank
    37.5 = 37.5%
  4. Calculate Active C fraction
    Active C fraction = (poxcMgPerKg / estimatedSOC) * 100
    3.5 = 3.5%

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