% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/diagnostics-horizons-usda.R
\name{argillic_clay_films_test}
\alias{argillic_clay_films_test}
\title{Test for clay-illuviation evidence (KST 13ed Ch 3 p 4)}
\usage{
argillic_clay_films_test(pedon)
}
\arguments{
\item{pedon}{A \code{\link{PedonRecord}}.}
}
\value{
A \code{\link{DiagnosticResult}}.
}
\description{
KST 13ed argillic horizon requires "evidence of illuvial accumulation
of clay" alongside the clay-increase rule. Acceptable evidence:
\itemize{
  \item oriented clays bridging sand grains in >= 1\% of the horizon;
  \item clay films lining pores or coating ped faces;
  \item lamellae more than 5 mm thick.
}
}
\details{
This test reads three complementary slots, in order of evidence strength:
\enumerate{
  \item \code{pedon$site$nasis_diagnostic_features} -- the NASIS
        \code{pediagfeatures.featkind} vector. The surveyor's
        explicit "Argillic horizon" entry directly confirms
        clay-illuviation evidence (~13 500 entries in the 2021
        NASIS snapshot). Strongest evidence.
  \item \code{pedon$horizons$clay_films_amount} -- per-horizon
        clay-film abundance derived from NASIS \code{phpvsf}.
        Values: \code{"few"}, \code{"common"}, \code{"many"},
        \code{"continuous"}. Direct measurement.
  \item \code{pedon$horizons$designation} containing a 't'
        master suffix (e.g. \code{Bt}, \code{Btk}, \code{Btx},
        \code{Bt1}, \code{2Bt}). v0.9.28: the pedologist who
        wrote that designation explicitly identified the
        horizon as clay-illuvial -- per KST 13ed Ch 18, the 't'
        suffix means "accumulation of silicate clay" -- so it
        counts as positive evidence even when NASIS records are
        absent. This unlocks the KST 13ed argillic thresholds
        for the ~47 % of KSSL profiles that lack NASIS
        pediagfeatures and phpvsf records.
}

Any of the three sources counts as positive evidence (logical OR).
\code{passed = NA} when none is populated AND no horizon designation
field is present at all (lab-only loaders without horizon
descriptions). \code{passed = FALSE} when designations exist but
none has a 't' suffix and NASIS slots are empty.
}
\references{
Soil Survey Staff (2022), Keys to Soil Taxonomy 13th
  ed., Ch. 3, argillic horizon (clay-illuviation criteria, p. 4);
  Ch. 18, master horizon symbols (\code{t}: silicate-clay
  accumulation, p. 332).
}
