  We study pion production in proton-proton collisions within a pQCD-improved
parton model in next-to-leading order augmented by intrinsic transverse
momentum ($k_\perp$) of the partons. We find the introduction of $k_\perp$
necessary to reproduce the experimental data in the CERN SPS to RHIC energy
range. We study the influence of intrinsic $k_\perp$ on the so-called $K$
factor, the ratio of the NLO cross section to the Born term. A strong $p_T$
dependence is seen, especially in the 3-6 GeV transverse momentum region of the
outgoing pion, where nuclear effects (e.g. the Cronin effect) play an important
role.
