Tests for the nitic horizon: a clay-rich (>= 30%), Fe-rich (DCB Fe >= 4%) subsurface horizon at least 30 cm thick. Diagnostic of Nitisols. WRB 2022 additionally requires polyhedral / nutty structure with shiny ped surfaces and a gradual (non-abrupt) clay decrease with depth.
Usage
nitic_horizon(
pedon,
min_clay = 30,
min_fe_dcb = 4,
min_thickness = 30,
max_clay_drop_pct = 8,
max_decrease_depth = 50
)Arguments
- pedon
A
PedonRecord.- min_clay
Minimum clay % (default 30).
- min_fe_dcb
Minimum DCB-extractable Fe % (default 4).
- min_thickness
Minimum thickness in cm (default 30).
- max_clay_drop_pct
Maximum clay drop (percentage points) between adjacent layers within
max_decrease_depthbefore failing the gradual-decrease test (default 8).- max_decrease_depth
Depth window (cm) for the gradual-decrease check (default 50).
Details
Required (AND-combined) sub-tests:
Profile does not have a ferralic horizon (Ferralsol path is canonical for the clay-rich + low-CEC corner).
clay % >=
min_clay.fe_dcb_pct >=
min_fe_dcb.thickness >=
min_thickness.
Supplementary (soft-AND) sub-tests – evaluated when evidence is present in the pedon, evaluate to NA (not a fail) when missing:
structure_type matches polyhedral / nutty / (sub)angular blocky.
slickensides / shiny ped surfaces present (proxy for WRB's "shiny ped surfaces").
clay does not decrease abruptly between adjacent layers within 50 cm of the surface (gradual-decrease pattern; drop > 8 percentage points fails).
Supplementary tests fail (return passed = FALSE) only when evidence actively contradicts the criterion; missing evidence is permissive.