Histic epipedon (USDA Soil Taxonomy, 13th edition) — histic_epipedon

A surface horizon (or layers within 40 cm of the surface) that is periodically saturated with water and has sufficiently high organic carbon to be considered organic soil material. Diagnostic for the Histosols order, the Histels suborder of Gelisols, and the Hist- modifier in many other taxa.

Usage

histic_epipedon_usda(
  pedon,
  min_oc_pct = 12,
  min_thickness_cm = 20,
  min_ap_oc_pct = 8
)

Arguments

pedon: A PedonRecord.
min_oc_pct: Minimum organic carbon percent for organic soil material (default 12; equivalent to ~20% organic matter per KST conversion factor 0.58).
min_thickness_cm: Minimum thickness (default 20 cm).
min_ap_oc_pct: Minimum OC for the Ap-horizon shortcut (default 8 percent).

Value

A DiagnosticResult.

Details

KST 13ed required characteristics (Ch. 3, pp 13-15):

Saturated 30+ days/year (or artificially drained); AND
Organic soil material that is either:
- 20-60 cm thick AND (Sphagnum >= 75 percent OR bulk_density < 0.1 g/cm3); OR
- 20-40 cm thick (general); OR
OR Ap horizon mixed to 25 cm with OC >= 8 percent by weight.

Implementation notes (v0.8.x):

Saturation is detected via a horizon designation starting with H (per KST notation) or via the WRB horizonte_glei as fallback when redoximorphic features are present.
Sphagnum content uses the WRB fiber_content_rubbed_pct column (>= 75 means very fibrous); refinement to a true Sphagnum-specific column is deferred.

References

Soil Survey Staff (2022). Keys to Soil Taxonomy, 13th edition, USDA-NRCS, Washington DC. Ch. 3, pp. 13-15.