% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/diagnostics-conditions-usda.R
\name{permafrost_within_usda}
\alias{permafrost_within_usda}
\title{Permafrost (USDA Soil Taxonomy, 13th edition)}
\usage{
permafrost_within_usda(pedon, max_top_cm = 100)
}
\arguments{
\item{pedon}{A \code{\link{PedonRecord}}.}

\item{max_top_cm}{Maximum depth where permafrost must occur
(default 100 cm -- Gelisols criterion at Order level).}
}
\value{
A \code{\link{DiagnosticResult}}.
}
\description{
"Permafrost is defined as a thermal condition in which a material
(including soil material) remains below 0 C for 2 or more years in
succession."  -- KST 13ed, Ch 3, p 47.
}
\details{
Permafrost is the defining characteristic of the Gelisols order
(within 100 cm of the soil surface) and qualifies many subgroups
across Histosols (Histels), Inceptisols, and others.

Implementation: Uses \code{permafrost_temp_C} from schema. A
layer qualifies as permafrost when its \code{permafrost_temp_C}
is <= 0 C. The function checks whether any qualifying layer
occurs within \code{max_top_cm} of the surface.
}
\references{
Soil Survey Staff (2022), KST 13ed, Ch. 3, p 47.
}
