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Melanic epipedon (USDA Soil Taxonomy, 13th edition)

Source: R/diagnostics-epipedons-usda.R
melanic_epipedon_usda.Rd

A thick, very dark, andic, organic-rich surface horizon associated with volcanic-ash-derived soils in cool, humid environments. Diagnostic for the Melanists / Melanudands great groups of Andisols.

Usage

melanic_epipedon_usda(pedon)

Arguments

pedon

A PedonRecord.

Value

A DiagnosticResult.

Details

KST 13ed required characteristics (Ch. 3, pp 15-16):

  • Upper boundary at or within 30 cm of the mineral soil surface (or organic layer with andic properties);

  • Cumulative thickness >= 30 cm within 40 cm with all of:

    • Andic soil properties throughout;

    • Color value <= 2.5 moist AND chroma <= 2 throughout;

    • Melanic index <= 1.70 (deferred – specialized lab measurement);

    • OC >= 6 percent (weighted) AND >= 4 percent (each layer).

Implementation notes (v0.8.x):

  • Andic soil properties are tested via andic_properties_usda (v0.9; for v0.8 we approximate with bulk_density <= 0.9 g/cm3 AND phosphate_retention >= 85%).

  • Melanic index (= 100 / (OC * 100 + 1) per KST appendix) is deferred – requires UV-Vis spectroscopy.

References

Soil Survey Staff (2022), KST 13ed, Ch. 3, pp 15-16.