Soil Protein Calculator
Interpret autoclave-citrate extractable (ACE) soil protein results to estimate nitrogen mineralization potential and fertilizer credits.
About this calculator
ACE soil protein — autoclaved citrate-extractable protein, developed by Hurisso et al. (2018) in Agricultural & Environmental Letters — measures the pool of organic nitrogen locked up in microbial biomass and readily decomposable organic matter, giving a direct read on how much plant-available nitrogen your soil biology is likely to release over a season. This calculator takes your lab-reported ACE protein value in mg per gram of soil and converts it into a nitrogen mineralization estimate using a coefficient of 0.15 (a midpoint of the commonly cited 0.12-0.18 range), scaled by your growing season length relative to a 150-day reference season. That mineralization rate is then converted to pounds of nitrogen per acre, assuming the top six inches of soil weighs about two million pounds per acre, and adjusted downward for clay content — clay minerals chemically bind and immobilize some of that mineralized nitrogen, making less of it available to crops.
From there, the calculator estimates a fertilizer nitrogen credit (about 65% of mineralized N reaching the crop) and its dollar value at roughly $0.60 per pound of nitrogen, letting you weigh reducing synthetic fertilizer against your soil's own biological supply. It also computes a protein-to-organic-matter ratio: a higher ratio signals your organic matter is more biologically active and nitrogen-rich per unit, rather than being mostly inert, humified carbon. As with any single-test interpretation, treat the fertilizer credit as a starting point for adjusting rates, not a substitute for a full nutrient management plan.
Inputs
Results
Protein rating (0-100)
50
Figures current as of 2018. Source: Hurisso, T.T., Moebius-Clune, D.J., Culman, S.W., Moebius-Clune, B.N., Thies, J.E., van Es, H.M. Soil Protein as a Rapid Soil Health Indicator of Potentially Available Organic Nitrogen. Agricultural & Environmental Letters. 2018;3(1):170098.
How to Use This Calculator
- Enter your ACE soil protein value from a lab test in mg protein per gram of dry soil.
- Input soil organic matter percentage and clay content.
- Set your growing season length in days.
- Review the Estimated Mineralizable Nitrogen and the Soil Protein Rating.
- Use the Recommended Nitrogen Credit to adjust synthetic fertilizer rates accordingly.
What each input means
- ACE soil protein (mg/g)
- Autoclave-citrate extractable protein from lab report (mg protein per g dry soil).
- Soil organic matter (%)
- SOM from standard soil test for protein:OM ratio calculation.
- Clay content (%)
- Percent clay in soil — higher clay stabilizes more N, reducing availability.
- Growing season length (days)
- Number of days in your growing season (frost-free period).
What each result means
- Protein rating (0-100)
- Overall soil protein rating from 0 (very low) to 100 (excellent).
- N mineralization (lb N/ac)
- Estimated nitrogen mineralized over the growing season.
- Fertilizer N credit (lb N/ac)
- Estimated plant-available N from soil biology (~65% of mineralized).
- Fertilizer value ($/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
- Identify Input Parameters4 parametersACE soil protein (mg/g) = 12, Soil organic matter (%) = 3, Clay content (%) = 25, Growing season length (days) = 150 = 4 input(s) provided
- Calculate Protein ratingProtein rating50 = 50
- Calculate N mineralizationN mineralization = nLbPerAcre * (1 - clayContent * 0.003)3.3 = 3.3
- Calculate Fertilizer N creditFertilizer N credit = adjustedNLbPerAcre * 0.652.2 = 2.2
Figures and sources
- Autoclaved citrate-extractable (ACE) soil protein method (2018) — Hurisso, T.T., Moebius-Clune, D.J., Culman, S.W., Moebius-Clune, B.N., Thies, J.E., van Es, H.M. Soil Protein as a Rapid Soil Health Indicator of Potentially Available Organic Nitrogen. Agricultural & Environmental Letters. 2018;3(1):170098.
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does a longer growing season increase the nitrogen mineralization estimate?
The calculator normalizes your growing season length against a 150-day reference using seasonFactor = growingSeasonDays / 150, then multiplies your ACE protein value by 0.15 and that season factor. A longer frost-free period gives soil microbes more time to mineralize the organic nitrogen represented by your ACE protein reading, so the same ACE protein value yields a proportionally higher total N mineralization estimate on a 200-day season than on a 100-day one.
Why does higher clay content reduce the plant-available nitrogen estimate?
Clay minerals have a strong capacity to chemically bind and immobilize ammonium and other mineralized nitrogen forms, holding onto some of that nitrogen instead of leaving it freely available for crop uptake. The calculator models this with adjustedNLbPerAcre = nLbPerAcre × (1 − clayContent × 0.003), so at 25% clay about 7.5% of the raw mineralization estimate is subtracted off, and that reduction grows as clay content rises.
What does the protein-to-organic-matter ratio actually indicate?
This calculator divides your ACE protein reading by your organic matter percentage to get proteinOMRatio, a measure of how nitrogen-rich and biologically active your organic matter is per unit, rather than how much organic matter you simply have. A high ratio (6+) means your organic matter is dominated by fresh, protein-rich, easily mineralizable material, while a low ratio suggests your organic matter is mostly older, more humified carbon that releases nitrogen more slowly.
Why is only 65% of the mineralized nitrogen counted as a fertilizer credit?
Not all nitrogen that mineralizes from soil organic matter over a season is captured by the crop — some is lost to leaching, denitrification, or immobilization by other soil processes before roots can take it up. The calculator applies a 65% availability factor to the clay-adjusted mineralization estimate to get fertilizerCreditLbN, reflecting a conservative estimate of how much of that biologically-supplied nitrogen crops can actually use to offset synthetic fertilizer.
Related Calculators
The questions that sit next to this one — chosen by subject, including calculators filed under a different category.
Cover Crop Biomass Calculator
Estimate above-ground biomass, carbon contribution, and nitrogen credits from cover crop species based on growing degree days.
Soil HealthActive Carbon Calculator
Permanganate-oxidizable carbon (POXC) from soil sample absorbance readings using the Weil et al. method.
Soil ScienceOrganic Matter Calculator
Calculate compost needed to raise soil organic matter, with estimates for water holding capacity improvement, CEC boost, and nitrogen mineralization.
Soil HealthWater Stable Aggregate Calculator
Calculate water-stable aggregate percentage from wet-sieving test results to assess soil structural health and erosion resistance.
Clinical NutritionNitrogen Balance Calculator
Calculate nitrogen balance from protein intake and 24-hour urinary urea nitrogen (UUN). Determine if a patient is in anabolic or catabolic state and find protein targets.
More in Agriculture & Farming.