  $\phi$ and K$^-$ mesons from Ni+Ni collisions at the beam energy of 1.91A GeV
have been measured by the FOPI spectrometer, with a trigger selecting central
and semi-central events amounting to 51% of the total cross section. The phase
space distributions, and the total yield of K$^-$, as well as the kinetic
energy distribution and the total yield of $\phi$ mesons are presented. The
$\phi$\K$^-$ ratio is found to be $0.44 \pm 0.07(\text{stat}) ^{+0.18}_{-0.12}
(\text{syst})$, meaning that about 22% of K$^-$ mesons originate from the
decays of $\phi$ mesons, occurring mostly in vacuum. The inverse slopes of
direct kaons are up to about 15 MeV larger than the ones extracted within the
one-source model, signalling that a considerable share of gap between the
slopes of K$^+$ and K$^-$ could be explained by the contribution of $\phi$
mesons to negative kaons.
