% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/diagnostics-epipedons-usda.R
\name{melanic_epipedon_usda}
\alias{melanic_epipedon_usda}
\title{Melanic epipedon (USDA Soil Taxonomy, 13th edition)}
\usage{
melanic_epipedon_usda(pedon)
}
\arguments{
\item{pedon}{A \code{\link{PedonRecord}}.}
}
\value{
A \code{\link{DiagnosticResult}}.
}
\description{
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.
}
\details{
KST 13ed required characteristics (Ch. 3, pp 15-16):
\itemize{
  \item Upper boundary at or within 30 cm of the mineral soil
        surface (or organic layer with andic properties);
  \item Cumulative thickness >= 30 cm within 40 cm with all of:
    \itemize{
      \item Andic soil properties throughout;
      \item Color value <= 2.5 moist AND chroma <= 2 throughout;
      \item Melanic index <= 1.70 (deferred -- specialized lab
            measurement);
      \item OC >= 6 percent (weighted) AND >= 4 percent (each
            layer).
    }
}

Implementation notes (v0.8.x):
\itemize{
  \item Andic soil properties are tested via \code{andic_properties_usda}
        (v0.9; for v0.8 we approximate with bulk_density <=
        0.9 g/cm3 AND phosphate_retention >= 85\%).
  \item 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.
}
