% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/diagnostics-horizons-wrb.R
\name{nitic_horizon}
\alias{nitic_horizon}
\title{Nitic horizon (WRB 2022)}
\usage{
nitic_horizon(
  pedon,
  min_clay = 30,
  min_fe_dcb = 4,
  min_thickness = 30,
  max_clay_drop_pct = 8,
  max_decrease_depth = 50
)
}
\arguments{
\item{pedon}{A \code{\link{PedonRecord}}.}

\item{min_clay}{Minimum clay \% (default 30).}

\item{min_fe_dcb}{Minimum DCB-extractable Fe \% (default 4).}

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

\item{max_clay_drop_pct}{Maximum clay drop (percentage points)
between adjacent layers within \code{max_decrease_depth}
before failing the gradual-decrease test (default 8).}

\item{max_decrease_depth}{Depth window (cm) for the gradual-decrease
check (default 50).}
}
\value{
A \code{\link{DiagnosticResult}}.
}
\description{
Tests for the nitic horizon: a clay-rich (>= 30\%), Fe-rich (DCB
Fe >= 4\%) subsurface horizon at least 30 cm thick. Diagnostic of
Nitisols. WRB 2022 additionally requires polyhedral / nutty
structure with shiny ped surfaces and a gradual (non-abrupt) clay
decrease with depth.
}
\details{
Required (AND-combined) sub-tests:
\itemize{
  \item Profile does not have a ferralic horizon (Ferralsol path
        is canonical for the clay-rich + low-CEC corner).
  \item clay \% >= \code{min_clay}.
  \item fe_dcb_pct >= \code{min_fe_dcb}.
  \item thickness >= \code{min_thickness}.
}

Supplementary (soft-AND) sub-tests -- evaluated when evidence is
present in the pedon, evaluate to NA (not a fail) when missing:
\itemize{
  \item structure_type matches polyhedral / nutty / (sub)angular
        blocky.
  \item slickensides / shiny ped surfaces present (proxy for
        WRB's "shiny ped surfaces").
  \item clay does not decrease abruptly between adjacent layers
        within 50 cm of the surface (gradual-decrease pattern;
        drop > 8 percentage points fails).
}
Supplementary tests fail (return passed = FALSE) only when evidence
actively contradicts the criterion; missing evidence is permissive.
}
\references{
IUSS Working Group WRB (2022), Chapter 3, Nitic horizon.
}
