Skip to contents

Test for clay-illuviation evidence (KST 13ed Ch 3 p 4)

Source: R/diagnostics-horizons-usda.R
argillic_clay_films_test.Rd

KST 13ed argillic horizon requires "evidence of illuvial accumulation of clay" alongside the clay-increase rule. Acceptable evidence:

  • oriented clays bridging sand grains in >= 1% of the horizon;

  • clay films lining pores or coating ped faces;

  • lamellae more than 5 mm thick.

Usage

argillic_clay_films_test(pedon)

Arguments

pedon

A PedonRecord.

Value

A DiagnosticResult.

Details

This test reads three complementary slots, in order of evidence strength:

  1. pedon$site$nasis_diagnostic_features – the NASIS pediagfeatures.featkind vector. The surveyor's explicit "Argillic horizon" entry directly confirms clay-illuviation evidence (~13 500 entries in the 2021 NASIS snapshot). Strongest evidence.

  2. pedon$horizons$clay_films_amount – per-horizon clay-film abundance derived from NASIS phpvsf. Values: "few", "common", "many", "continuous". Direct measurement.

  3. pedon$horizons$designation containing a 't' master suffix (e.g. Bt, Btk, Btx, Bt1, 2Bt). v0.9.28: the pedologist who wrote that designation explicitly identified the horizon as clay-illuvial – per KST 13ed Ch 18, the 't' suffix means "accumulation of silicate clay" – so it counts as positive evidence even when NASIS records are absent. This unlocks the KST 13ed argillic thresholds for the ~47 pediagfeatures and phpvsf records.

Any of the three sources counts as positive evidence (logical OR). passed = NA when none is populated AND no horizon designation field is present at all (lab-only loaders without horizon descriptions). passed = FALSE when designations exist but none has a 't' suffix and NASIS slots are empty.

References

Soil Survey Staff (2022), Keys to Soil Taxonomy 13th ed., Ch. 3, argillic horizon (clay-illuviation criteria, p. 4); Ch. 18, master horizon symbols (t: silicate-clay accumulation, p. 332).