  We study the Schwinger mechanism in QCD in the presence of an arbitrary
time-dependent chromo-electric background field $E^a(t)$ with arbitrary color
index $a$=1,2,...8 in SU(3). We obtain an exact result for the non-perturbative
quark (antiquark) production from an arbitrary $E^a(t)$ by directly evaluating
the path integral. We find that the exact result is independent of all the time
derivatives $\frac{d^nE^a(t)}{dt^n}$ where $n=1,2,...\infty$. This result has
the same functional dependence on two Casimir invariants $[E^a(t)E^a(t)]$ and
$[d_{abc}E^a(t)E^b(t)E^c(t)]^2$ as the constant chromo-electric field $E^a$
result with the replacement: $E^a \rightarrow E^a(t)$. This result relies
crucially on the validity of the shift conjecture, which has not yet been
established.
