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Irrigation EC M2b: phosphate coefficients fitted to Pethybridge et al. 2006 - #30
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Irrigation EC M2b: phosphate coefficients fitted to Pethybridge et al. 2006
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Summary
Irrigation EC M2b: H₂PO₄⁻ and HPO₄²⁻ now have 25 °C conductivity coefficients fitted to measured data. This narrows the bounded EC ranges from M2a.
O1 amended (design §11, §13). Muccitelli & DiAngelo (1994) has no lawful open copy, so the fit uses the open data of Pethybridge, Talbot & House, J. Solution Chem. 35(3), 381–393 (2006), doi 10.1007/s10953-005-9003-z, Table III.
Method. Each of the 22 KH₂PO₄ and ½K₂HPO₄ points is speciated with FlahaX. λ° and A are fitted with B fixed at 1.5 (
tools/fit_phosphate_conductivity.py):RMS is 0.127 % and the worst point is −0.27 %. The data reach I = 0.014 mol/kgw; use above that is extrapolated and recorded in the audit.
Reproducibility. The tool reproduces the shipped coefficient block byte-for-byte from the fixture, and the file is SHA-pinned. The coefficients sit in a separate
supplementaryblock, are valid at 25 °C only, and leave the McCleskey table untouched.Transcription. The owner's transcription of Table III agrees with an independent transcription from the PDF on all 26 values, and the citation was confirmed from the PDF.
Cross-checks (reported, all within 15 %):
phreeqc.datWhat stays bounded. PO₄³⁻ and minor pairs such as KHPO₄⁻ remain under the O2 bound. KHPO₄⁻'s current is partly absorbed by the HPO₄²⁻ fit, so the upper end of a range may count it twice; this is small, conservative and documented.
Effect. All 26 shipped formulas are
estimated, with the widest range now 5.4 % of the midpoint, down from 14.4 % under M2a.MODEL_VERSIONis nowirrigation-ec-mccleskey2012-m2b-experimental.Test plan
--checkpass