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Mollic epipedon (USDA Soil Taxonomy, 13th edition)

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

A thick, dark-colored, base-rich mineral surface horizon. The principal diagnostic horizon of the Mollisols order; also qualifies many subgroups of other orders as "Mollic" or "Pachic".

Usage

mollic_epipedon_usda(pedon, min_bs = 50, min_oc_pct = 0.6)

Arguments

pedon

A PedonRecord.

min_bs

Default 50 percent.

min_oc_pct

Default 0.6 percent.

Value

A DiagnosticResult.

Details

KST 13ed required characteristics (Ch. 3, pp 15-17):

  • Color: dominant color value <= 3 (moist) AND <= 5 (dry) AND chroma <= 3 (moist), with adjustments for CaCO3 content (deferred to v0.9);

  • Base saturation (NH4OAc, pH 7) >= 50 percent throughout;

  • Organic carbon >= 0.6 percent (or 2.5 percent if value is 4-5 moist; or 0.6 absolute > C horizon);

  • Thickness: 18 cm general, 25 cm if texture is loamy fine sand or coarser, 10 cm if directly above lithic/densic/ paralithic contact (thin_lithic_overlay branch);

  • Structure: peds <= 30 cm OR rupture-resistance <= moderately hard;

  • Some part moist 90+ days when soil temp at 50 cm is >= 5 C (deferred – requires climatic data).

Implementation notes (v0.8.x):

  • Thickness rule is computed dynamically based on texture and presence of underlying lithic/paralithic contact.

  • N value < 0.7 / fluidity nonfluid is assumed (laboratory tests rarely available);

  • 90-day moisture condition is deferred to v0.9.

References

Soil Survey Staff (2022), KST 13ed, Ch. 3, pp 15-17.