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Nitic horizon (WRB 2022)

Source: R/diagnostics-horizons-wrb.R
nitic_horizon.Rd

Tests for a nitic horizon, WRB 2022 Chapter 3.1.22, criterion by criterion on each layer:

  1. \(\ge\) 30% clay (min_clay);

  2. moderate to strong angular or subangular blocky structure breaking into polyhedral or flat-edged second-level structure, or polyhedral structure, with pressure faces (shiny surfaces) on \(\ge\) 25% of the aggregate surfaces. Read from structure_type, structure_grade, structure_type_secondary and pressure_faces, "common" or more (since v0.9.317; until then from clay films, which WRB 2022 keeps apart from pressure faces);

  3. \(\ge\) 4% Fe-dith (fe_dcb_pct), \(\ge\) 0.2% Fe-ox (fe_ox_pct) and Fe-ox / Fe-dith \(\ge\) 0.05;

  4. not part of a plinthic horizon (plinthic);

  5. the layers that meet 1-4 are \(\ge\) 30 cm thick together, as one horizon (min_thickness).

A criterion is FALSE when the data contradict it and NA when the data it needs are missing: a profile without Fe-ox or structure records gets NA, not a nitic horizon. With options(soilKey.morphological_inference = TRUE) missing structure and Fe data are read from a Bt designation with a CEC of 8-36 cmolc/kg clay and no albic E above (the v0.9.18 reading of legacy profiles), recorded in the evidence.

Usage

nitic_horizon(
  pedon,
  min_clay = 30,
  min_fe_dcb = 4,
  min_thickness = 30,
  min_fe_ox = 0.2,
  min_feox_fedith = 0.05,
  max_clay_drop_pct = NULL,
  max_decrease_depth = NULL
)

Arguments

pedon

A PedonRecord.

min_clay

Minimum clay % (default 30).

min_fe_dcb

Minimum dithionite Fe % (default 4).

min_thickness

Minimum thickness in cm (default 30).

min_fe_ox

Minimum oxalate Fe % (default 0.2).

min_feox_fedith

Minimum Fe-ox / Fe-dith ratio (default 0.05).

max_clay_drop_pct, max_decrease_depth

Unused since v0.9.220, kept so that existing calls still run.

Value

A DiagnosticResult.

Details

Until v0.9.219 the structure and shiny-surface tests never vetoed, Fe-ox was not read, a plinthic horizon was not excluded, any ferralic horizon in the profile excluded a nitic one (WRB 2022 does not: Nitisols key out before Ferralsols), the Fe inference above ran by default, and a clay drop of more than 8 percentage points within 50 cm vetoed it. The clay rule of the Nitisol key is in nitisol.

References

IUSS Working Group WRB (2022), Chapter 3.1.22, Nitic horizon.