% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/diagnostics-epipedons-usda.R
\name{histic_epipedon_usda}
\alias{histic_epipedon_usda}
\title{Histic epipedon (USDA Soil Taxonomy, 13th edition)}
\usage{
histic_epipedon_usda(
  pedon,
  min_oc_pct = 12,
  min_thickness_cm = 20,
  min_ap_oc_pct = 8
)
}
\arguments{
\item{pedon}{A \code{\link{PedonRecord}}.}

\item{min_oc_pct}{Minimum organic carbon percent for organic soil
material (default 12; equivalent to ~20\% organic matter
per KST conversion factor 0.58).}

\item{min_thickness_cm}{Minimum thickness (default 20 cm).}

\item{min_ap_oc_pct}{Minimum OC for the Ap-horizon shortcut
(default 8 percent).}
}
\value{
A \code{\link{DiagnosticResult}}.
}
\description{
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.
}
\details{
KST 13ed required characteristics (Ch. 3, pp 13-15):
\itemize{
  \item Saturated 30+ days/year (or artificially drained); AND
  \item Organic soil material that is either:
    \itemize{
      \item 20-60 cm thick AND (Sphagnum >= 75 percent OR
            bulk_density < 0.1 g/cm3); OR
      \item 20-40 cm thick (general); OR
    }
  \item OR Ap horizon mixed to 25 cm with OC >= 8 percent by weight.
}

Implementation notes (v0.8.x):
\itemize{
  \item Saturation is detected via a horizon designation
        starting with H (per KST notation) or via the WRB
        \code{horizonte_glei} as fallback when redoximorphic
        features are present.
  \item Sphagnum content uses the WRB \code{fiber_content_rubbed_pct}
        column (>= 75 means very fibrous); refinement to a true
        Sphagnum-specific column is deferred.
}
}
\references{
Soil Survey Staff (2022). \emph{Keys to Soil Taxonomy},
  13th edition, USDA-NRCS, Washington DC. Ch. 3, pp. 13-15.
}
