  Inclusive cross section for pion production in proton - proton collisions are
calculated based on unintegrated parton distribution functions (uPDFs). In
addition to purely gluonic terms the present approach includes also quark
degrees of freedom. Phenomenological fragmentation functions from the
literature are used. The new mechanisms are responsible for $\pi^+$ - $\pi^-$
asymmetry. In contrast to standard collinear approach, application of 2 $\to$ 1
$k_t$ - factorization approach can be extended towards much lower transverse
momenta, both at mid and forward rapidity region. The results of the
calculation are compared with SPS and RHIC data.
