  The UrQMD transport model is used to study a system-size and energy
dependence of the pion production in high energy collisions. New data of the
NA61/SHINE Collaboration on spectra of negatively charged pions in
proton-proton interactions at SPS energies are considered. These results are
compared with the corresponding data of the NA49 Collaboration in central Pb+Pb
collisions at the same collision energies per nucleon. Mean pion multiplicity
per participant nucleon, inverse slope parameter of the transverse momentum
spectra, and width of rapidity distribution are investigated. A role of isospin
effects is discussed. We find that the UrQMD model predicts a non-monotonous
behavior of mean transverse mass with collision energy for positively charged
pions at the mid-rapidity in inelastic proton-proton interactions. This will be
checked soon experimentally by NA61/SHINE Collaboration.
