Calculator sources
Every calculator on this site prints the publications its method comes from, but they sit at the bottom of the tool where they are easy to miss. This register puts all of them in one place: each tool, each citation that tool names, and a link to the source itself where the publisher still serves one.
Nothing here is a reference we inferred afterwards. The rows are transcribed from the reference blocks the calculators already print, so what the register lists and what the tool cites are the same list. Where a tool publishes no outside source, that is stated instead of filled in.
How the links were checked
Each address below was fetched on 29 September 2026 with a browser user agent, following redirects, and only kept when it answered HTTP 200. Hosts that block automated traffic were opened in a headless Chromium session instead; a source that would not serve a real browser was left out rather than guessed at. An empty link cell reads “Printed reference”, which means the citation is real and published but the address is behind a paywall, has been retired, or never existed as a stable page: we cite the work, and we do not invent a URL for it.
Turn buffering capacity (CEC, buffer pH or OM%) into tons of ag lime per acre, adjusted for ECCE and ENV.
| Citation | Type | Link |
|---|---|---|
| Conservation Practice Standard: Nutrient Management (Code 590), 2020 | Standard | USDA Natural Resources Conservation Service |
| Shoemaker, H. E., McLean, E. O. & Pratt, P. F. (1961). Buffer Methods for Determining Lime Requirement of Soils. Soil Science Society of America Journal 25(4), 274-277. | Journal article | Printed reference |
| Soil Acidity and Liming for Agricultural Soils, Agronomy Guide | Extension bulletin | Penn State Extension |
| Soil Testing and Interpretations: Lime Requirement Calculations, Bulletin 1348 | Extension bulletin | Printed reference |
Elemental sulfur, iron or aluminum rates to hit a target pH — with acidifier comparison and rebound warnings.
| Citation | Type | Link |
|---|---|---|
| No external publication is named by this tool. The rate multipliers, burn limits and split-dose rules are printed in-page under Application Plan and the acidifier comparison table. | In-page method | Printed reference |
This tool names no outside publication, so nothing has been attributed to it: the method it prints is the method it uses, and the register shows the limits it publishes rather than a source it never cited.
Formulate multi-nutrient dry and liquid N-P-K-S blends with carrier rates, costing and multi-element credits.
| Citation | Type | Link |
|---|---|---|
| Official Publication of the Association of American Plant Food Control Officials - Uniform State Fertilizer Bill and Rules | Standard | AAPFCO |
| Fertilizer Salt Index and Seed Safety Guidelines, Pub. AY-318-W | Extension bulletin | Purdue University Extension |
| Managing Nitrogen Volatilization and Inhibitor Technology, Pub. CROP 3073 | Extension bulletin | Printed reference |
| Liquid Fertilizer Formulation and Density Conversions, Pub. SL-132 | Extension bulletin | Printed reference |
| Spray Nozzle Selection and Density Liquid Conversion Factors, Catalog 51A - linked to the live catalogue index | Industry reference | TeeJet Technologies |
Convert lab ppm to meq/100g and read total CEC, base saturation and cation balance from one soil test.
| Citation | Type | Link |
|---|---|---|
| USDA-NRCS standard models - lab summation and the (OM% x 2.0) + (Clay% x 0.5) texture estimate, as stated on the tool | Standard | Printed reference |
The tool carries its USDA-NRCS model label in-page; the cation summation and texture estimate it runs are shown in its Method section.
Balance Ca, Mg, K and Na against Albrecht targets with a saturation donut, what-if simulator and plan.
| Citation | Type | Link |
|---|---|---|
| Conservation Practice Standard: Nutrient Management (Code 590) - base saturation and sodic soil guidance | Standard | USDA Natural Resources Conservation Service |
| Albrecht, W. A. (1975). Soil Fertility and Organic Action | Book or chapter | Printed reference |
| Kinsey, N. & Walters, C. (2009). Hands-On Agronomy: Base Saturation and Soil Cation Studies | Book or chapter | Printed reference |
| Brady, N. C. & Weil, R. R. (2017). The Nature and Properties of Soils, 15th edition - cation exchange and flocculation | Book or chapter | Printed reference |
| Fixen, P. E. & Grove, J. H. (1990). Testing Soils for Phosphorus and Potassium, in Soil Testing: Sampling, Correlation, Calibration, and Interpretation | Book or chapter | Printed reference |
| Eckert, D. J. & Watson, M. E. (1996). A Contemporary Look at the Albrecht Soil Fertility Philosophies. Journal of Production Agriculture 9(4) | Journal article | Printed reference |
Sodic soil reclamation: exchangeable sodium percentage into tons of gypsum per acre by source purity.
| Citation | Type | Link |
|---|---|---|
| Agriculture Handbook No. 60, Diagnosis and Improvement of Saline and Alkali Soils - gypsum requirement model | Agency publication | USDA Salinity Laboratory |
| Management of Sodic Soils, FAO Soils Bulletin - ESP/CEC amendment models and leaching requirements | Agency publication | Printed reference |
| Managing Sodic Soils, Fact Sheet 0.509 | Extension bulletin | Printed reference |
| Sodic Soils and Gypsum Amendments in Arid Agriculture | Extension bulletin | Printed reference |
Irrigation water quality — sodium adsorption ratio, CROSS and adjusted SAR with dispersion diagnostics.
| Citation | Type | Link |
|---|---|---|
| Agriculture Handbook No. 60, Diagnosis and Improvement of Saline and Alkali Soils - sodium adsorption ratio method | Agency publication | USDA Salinity Laboratory |
| Water Quality for Agriculture, Irrigation and Drainage Paper 29 | Agency publication | FAO |
| Suarez, D. L. (1981) - calcite-adjustment equilibrium model for adjusted SAR | Journal article | Printed reference |
| Rengasamy, P. & Marchuk, A. (2011) - CROSS, the cation ratio of soil structure | Journal article | Printed reference |
Element PPM in to salt grams and EC out for hydroponic reservoirs, with supplied-element tracking.
| Citation | Type | Link |
|---|---|---|
| Steiner, A. (1961). The universal nutrient solution - baseline macro and micro targets for fruiting crops | Journal article | Printed reference |
| Resh, H. Hydroponic Food Production - crop-specific ppm tables and reservoir management | Book or chapter | Printed reference |
| CRC Handbook of Chemistry and Physics - limiting molar ionic conductivities at 25 C | Book or chapter | Printed reference |
| CEAC hydroponics and Utah State University reservoir protocols - EC verification and stock handling | Extension bulletin | Printed reference |
Any one of pH, [H+], pOH or [OH-] into the whole equilibrium, with soil target ranges for that value.
| Citation | Type | Link |
|---|---|---|
| Gold Book - operational definition of pH and the activity basis of the scale | Standard | Printed reference |
| Richards, L. A. (1954). Diagnosis and Improvement of Saline and Alkali Soils, Agriculture Handbook No. 60 - soil reaction methods | Agency publication | USDA Salinity Laboratory |
| McLean, E. O. (1982). Soil pH and lime requirement, in Methods of Soil Analysis, Part 2 (ASA Monograph 9) | Book or chapter | Printed reference |
| Soil and Water Testing for Analytical Laboratories, FAO Soils Bulletin | Agency publication | Printed reference |
Exchangeable sodium percentage from Na and CEC in meq/100g or ppm, with the 6% and 15% sodicity thresholds.
| Citation | Type | Link |
|---|---|---|
| Richards, L. A. (1954). Diagnosis and Improvement of Saline and Alkali Soils, Agriculture Handbook No. 60 - the ESP at or above 15 percent definition | Agency publication | USDA Salinity Laboratory |
| Brady, N. C. & Weil, R. R. The Nature and Properties of Soils - sodicity thresholds, dispersion and reclamation | Book or chapter | Printed reference |
| Rengasamy, P. (2006). World salinity and sodicity problems, in Salinization of Land and Water Resources | Book or chapter | Printed reference |
| Sumner, M. E. & Naidu, R. (1998). Sodic Soils: Distribution, Properties, Management, and Environmental Consequences | Book or chapter | Printed reference |
How this register is kept honest
Two rules hold it together. First, a link only exists while it answers: when a publisher moves a bulletin, the address is dropped on the next re-check rather than left to rot, and the citation stays as text. Second, the register is not a claim that every figure on this site came from a linked page — journal papers and out-of-print books are cited by title, author and year because that is how the work is addressable.
The calculators themselves remain the primary record: each one prints its formula, its constants and the reference block this register mirrors. Dates, retractions and rewritten sections are logged on the corrections page. If a citation here looks wrong — wrong number, wrong title, source that no longer says what we lean on it for — tell us on the contact page and it gets checked against the publication, not defended.