% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/diagnostics-horizons-wrb.R
\name{ferralic}
\alias{ferralic}
\title{Ferralic horizon (WRB 2022)}
\usage{
ferralic(pedon, min_thickness = 30, max_cec = NULL, engine = NULL)
}
\arguments{
\item{pedon}{A \code{\link{PedonRecord}}.}

\item{min_thickness}{Minimum thickness in cm (default 30).}

\item{max_cec}{Maximum CEC (1M NH4OAc, pH 7) per kg clay
(default \code{NULL} = 16 in soilkey engine, 20 in aqp
engine; see \code{engine}).}

\item{engine}{One of \code{"soilkey"} (default; strict 16
cmol_c/kg-clay threshold per WRB 2022) or \code{"aqp"}
(relaxed 20 cmol_c/kg-clay -- a regional tolerance that
accommodates Brazilian / SOTERLAC Latossolos data, where
Embrapa-style Mehlich/Ca+Mg+K+Al sum often reads ~17-20
on profiles that the canonical NRCS / WRB definition would
accept as ferralic). \code{NULL} reads
\code{getOption("soilKey.diagnostic_engine")}. The numeric
threshold can also be overridden directly via
\code{options(soilKey.ferralic_max_cec = ...)}.}
}
\value{
A \code{\link{DiagnosticResult}}.
}
\description{
Tests whether any horizon meets the ferralic horizon criteria. The
ferralic horizon is a subsurface horizon resulting from long and
intense weathering, characterized by very low cation exchange capacity
per unit clay -- the canonical "low-activity clay" signal that defines
the Ferralsol RSG.
}
\details{
Sub-tests called:
\itemize{
  \item \code{test_ferralic_texture} -- texture sandy loam or
        finer.
  \item \code{test_cec_per_clay} -- CEC / clay <= 16 (or 20
        under \code{engine = "aqp"}) cmol_c/kg clay.
  \item \code{test_ferralic_thickness} -- thickness >= 30 cm.
}

v0.3.1 alignment with WRB 2022 Ch 3.1.10 (p. 44): the older
"ECEC <= 12 cmol_c/kg clay" gate was removed because it is not in the
canonical text -- only CEC (1M NH4OAc, pH 7) <= 16 is required.

v0.9.67 regional tolerance: BDsolos RJ benchmark (n=722 perfis)
showed 88/115 Latossolos failing the strict 16-cmol gate because
Embrapa lab methodology often reads CEC at 17-20 on profiles that
are unambiguously Latossolos by every other criterion. The
\code{engine = "aqp"} threshold of 20 closes that gap without
redefining the WRB threshold itself; users targeting strict
WRB 2022 fidelity should keep \code{engine = "soilkey"}.

The weatherable-mineral test (<= 10\% by volume),
water-dispersible-clay test, and stratification / rock-structure
exclusions remain deferred (they need mineralogical data outside
the canonical horizon schema) and are refinements rather than gates.
}
\references{
IUSS Working Group WRB (2022). \emph{World Reference Base
for Soil Resources}, 4th edition. International Union of Soil Sciences,
Vienna. Chapter 3.1.10 -- Ferralic horizon (p. 44).
}
