  We apply a Boltzmann approach to the kinetic regime of a relativistic
Bose-Einstein condensate of scalar bosons by decomposing the one-particle
distribution function in a condensate part and a non-zero momentum part of
excited modes, leading to a coupled set of evolution equations which are then
solved efficiently with an adaptive higher order Runge-Kutta scheme. We compare
our results to the partonic cascade Monte-Carlo simulation BAMPS for a critical
but far from equilibrium case of massless bosons. Motivated by the color glass
condensate initial conditions in QCD with a strongly overpopulated initial
glasma state, we also discuss the time evolution starting from an overpopulated
initial distribution function of massive scalar bosons. In this system a
self-similar evolution of the particle cascade with a non-relativistic
turbulent scaling in the infrared sector is observed as well as a relativistic
exponent for the direct energy cascade, confirming a weak wave turbulence in
the ultraviolet region.
