Plinthic horizon (WRB 2022)

Tests whether any horizon meets the plinthic horizon criteria. Plinthite is Fe-rich material that hardens irreversibly on repeated wetting and drying; the plinthic horizon is the diagnostic of Plinthosols.

Usage

plinthic(pedon, min_thickness = 15, min_plinthite_pct = 15)

Arguments

pedon

A PedonRecord.

min_thickness

Minimum thickness in cm (default 15).

min_plinthite_pct

Minimum volume % plinthite (default 15).

Value

A DiagnosticResult.

Details

Sub-tests:

• test_plinthite_concentration – plinthite volume % >= 15

• test_minimum_thickness – thickness >= 15 cm

v0.2 limitations: WRB 2022 also accepts profiles with >= 40% red Fe-rich mottles as alternative criterion – not yet wired. The "irreversibly hardens" criterion is conceptual and requires field observation; v0.2 takes plinthite_pct as already representing true plinthite (as opposed to soft mottles).

v0.9.72 designation morphological inference (opt-in)

Field-described Brazilian Plintossolos profiles (e.g.\ the Embrapa Redape curated dataset) routinely encode plinthite via the designation suffix f in the master letter sequence (e.g.\ Btf, 2Btf, Cf) – the curator's direct assertion that plinthite is present – without recording plinthite_pct as a numeric volume percent.

With options(soilKey.plinthic_designation_inference = TRUE) the function accepts a layer as plinthic when:

1. the canonical plinthite_pct test is NA for that layer, AND

2. the designation matches [A-Z]+[A-Za-z]*f[0-9]? (a f master-letter modifier in any sub-position).

Default is FALSE (canonical behaviour preserved).

References

IUSS Working Group WRB (2022), Chapter 3, Plinthic horizon.