Plaggic horizon (WRB 2022): sod-derived topsoil >= 20 cm with low BD AND independent evidence of human input.

v0.9.2.C tightening: the v0.3.3 implementation accepted ANY thick, low-BD, OC-rich A horizon, which over-fired across natural mollic / umbric / chernic surfaces. The diagnostic now requires, in addition to the OC + BD + thickness baseline, at least one independent anthropogenic-input marker:

• p_mehlich3_mg_kg >= 50 (sustained sod / manure additions concentrate Mehlich-3 P in the topsoil), OR

• artefacts_pct > 0 (any human artefact volume fraction is sufficient as a presence signal), OR

• designation pattern Apl / Aplg / Apk / explicit "plagg".

Without one of those markers the diagnostic returns FALSE even when OC + BD + thickness pass. This mirrors the v0.9.1 qual_plaggic gate but enforces the rule at the diagnostic level so any caller (SiBCS, USDA, future modules) inherits the protection.

Usage

plaggic(
  pedon,
  min_thickness = 20,
  max_bd = 1.5,
  min_oc = 0.6,
  min_p_mehlich3 = 50
)

Arguments

pedon

A PedonRecord.

min_thickness

Numeric threshold or option (see Details).

max_bd

Numeric threshold or option (see Details).

min_oc

Numeric threshold or option (see Details).

min_p_mehlich3

Numeric threshold or option (see Details).