Umbric horizon (WRB 2022) — umbric

Tests for the umbric horizon – a thick, dark, organic-rich surface horizon like mollic, but with low base saturation (< 50%). Diagnostic of Umbrisols.

Usage

umbric_horizon(
  pedon,
  min_thickness = 20,
  min_oc = 0.6,
  max_bs = 50,
  surface_top_cm = 5
)

Arguments

pedon: A PedonRecord.
min_thickness: Minimum thickness (cm; default 20).
min_oc: Minimum SOC % (default 0.6).
max_bs: Maximum base saturation % (default 50; profile must be BELOW this).
surface_top_cm: Maximum depth (cm) below the mineral soil surface at which the stack may start (default 5).

Value

A DiagnosticResult.

Details

Implementation reuses the mollic sub-tests on the contiguous stack of dark layers from the mineral soil surface (organic layers on top are not part of it), and tests the weighted average base saturation of the stack against max_bs (WRB 2022 3.1.39, pp. 69-70).

References

IUSS Working Group WRB (2022), Chapter 3.1.39, Umbric horizon (pp. 69-70).