  We investigate the effects of boost invariance breaking on the isotropization
of pressure in the glasma, using the $3+1$D glasma simulation. The breaking is
attributed to spatial fluctuations of the classical color charge density along
the collision axis. We present numerical results for pressure and energy
density at mid-rapidity and across a wider rapidity region. It is found that,
despite varying longitudinal correlation lengths, the behaviors of the pressure
isotropizations are qualitatively similar. The numerical results suggest that,
in the initial stage, longitudinal color electromagnetic fields develop,
similar to those in the boost invariant glasma. Subsequently, these fields
evolve into a dilute glasma, expanding longitudinally in a manner akin to a
dilute gas. We also show that the energy density at mid-rapidity exhibits a
$1/\tau$ decay in the dilute glasma stage.
