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Calcimator

Soil Protein Calculator

Interpret autoclave-citrate extractable (ACE) soil protein results to estimate nitrogen mineralization potential and fertilizer credits.

Inputs

%
%

Results

Protein rating (0-100)

50

N mineralization (lb N/ac)3.3
Fertilizer N credit (lb N/ac)2.2
Fertilizer value ($/ac)$1.00
Protein:OM ratio4
ACE protein (mg/g)12
RatingModerate
Om QualityGood quality
How to Use This Calculator
  1. Enter your ACE soil protein index (SPI) value from a lab test in mg/kg.
  2. Input soil texture class and land use history.
  3. Set your target nitrogen-release goal in lbs per acre.
  4. Review the Estimated Mineralizable Nitrogen and the Soil Protein Rating.
  5. Use the Recommended Nitrogen Credit to adjust synthetic fertilizer rates accordingly.

What each input means

ACE soil protein (mg/g)
Autoclave-citrate extractable protein from lab report (mg protein per g dry soil).
Soil organic matter (%)
SOM from standard soil test for protein:OM ratio calculation.
Clay content (%)
Percent clay in soil — higher clay stabilizes more N, reducing availability.
Growing season length (days)
Number of days in your growing season (frost-free period).

What each result means

Protein rating (0-100)
Overall soil protein rating from 0 (very low) to 100 (excellent).
N mineralization (lb N/ac)
Estimated nitrogen mineralized over the growing season.
Fertilizer N credit (lb N/ac)
Estimated plant-available N from soil biology (~65% of mineralized).
Fertilizer value ($/ac)
Dollar value of biological N at ~$0.60/lb N.
Protein:OM ratio
Higher ratio indicates more biologically active organic matter.
ACE protein (mg/g)
Your input ACE protein value for reference.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    ACE soil protein (mg/g) = 12, Soil organic matter (%) = 3, Clay content (%) = 25, Growing season length (days) = 150 = 4 input(s) provided
  2. Calculate Protein rating
    Protein rating
    50 = 50
  3. Calculate N mineralization
    N mineralization = nLbPerAcre * (1 - clayContent * 0.003)
    3.3 = 3.3
  4. Calculate Fertilizer N credit
    Fertilizer N credit = adjustedNLbPerAcre * 0.65
    2.2 = 2.2

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