  We investigate the Fe, C, N, O, Mg, Al, Si, K, Ca, Ce and Nd abundances of
2283 red giant stars in 31 globular clusters from high-resolution spectra
observed in both the northern and southern hemisphere by the SDSS-IV APOGEE-2
survey. This unprecedented homogeneous dataset, largest to date, allows us to
discuss the intrinsic Fe spread, the shape and statistics of Al-Mg and N-C
anticorrelations as a function of cluster mass, luminosity, age and metallicity
for all 31 clusters. We find that the Fe spread does not depend on these
parameters within our uncertainties including cluster metallicity,
contradicting earlier observations. We do not confirm the metallicity
variations previously observed in M22 and NGC 1851. Some clusters show a
bimodal Al distribution, while others exhibit a continuous distribution as has
been previously reported in the literature. We confirm more than 2 populations
in $\omega$ Cen and NGC 6752, and find new ones in M79. We discuss the scatter
of Al by implementing a correction to the standard chemical evolution of Al in
the Milky Way. After correction, its dependence on cluster mass is increased
suggesting that the extent of Al enrichment as a function of mass was
suppressed before the correction. We observe a turnover in the Mg-Al
anticorrelation at very low Mg in $\omega$ Cen, similar to the pattern
previously reported in M15 and M92. $\omega$ Cen may also have a weak K-Mg
anticorrelation, and if confirmed, it would be only the third cluster known to
show such a pattern.
