A hadronic
non-equilibrium model is proposed for describing the
relative abundance of strange particles in ultra-relativistic
heavy-ion collisions. We study the dependence of the multiplicity
ratios of charged kaons and lambdas on energy and baryon density
of the fireball and its total lifetime. It is demonstrated that
the sharp peak in positively charged K/pi ratio can be reproduced
if the fireball lifetime decreases with increasing beam energy due
to a weaker stopping.