  The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has
observed $\sim$600 transiting exoplanets and exoplanet candidates from
\textit{Kepler} (Kepler Objects of Interest, KOIs), most with $\geq$18 epochs.
The combined multi-epoch spectra are of high signal-to-noise (typically
$\geq$100) and yield precise stellar parameters and chemical abundances. We
first confirm the ability of the APOGEE abundance pipeline, ASPCAP, to derive
reliable [Fe/H] and effective temperatures for FGK dwarf stars -- the primary
\textit{Kepler} host stellar type -- by comparing the ASPCAP-derived stellar
parameters to those from independent high-resolution spectroscopic
characterizations for 221 dwarf stars in the literature. With a sample of 282
close-in ($P<100$ days) KOIs observed in the APOGEE KOI goal program, we find a
correlation between orbital period and host star [Fe/H] characterized by a
critical period, $P_\mathrm{crit}$= $8.3^{+0.1}_{-4.1}$ days, below which small
exoplanets orbit statistically more metal-enriched host stars. This effect may
trace a metallicity dependence of the protoplanetary disk inner-radius at the
time of planet formation or may be a result of rocky planet ingestion driven by
inward planetary migration. We also consider that this may trace a metallicity
dependence of the dust sublimation radius, but find no statistically
significant correlation with host $T_\mathrm{eff}$ and orbital period to
support such a claim.
