  We discuss the role of unfavoured light quark/antiquark to $D$ meson
fragmentation. The unknown parameters of fragmentation process are adjusted to
describe the asymmetry for $D^+$ and $D^-$ production measured by the LHCb.
Predictions for similar asymmetry for neutral $D$ mesons are presented. The
predicted asymmetry at large rapidity (or $x_F$) are very large which is
related to the valence-quark contribution. As a result, prompt atmospheric
neutrino flux at high neutrino energies can be much larger than for the
conventional $c \to D$ fragmentation. We predict large rapidity-dependent
$D^+/D^-$ and $D^0/{\bar D}^0$ asymmetries for low ($\sqrt{s} =$ 20 - 100 GeV)
energies. The $q/\bar q \to D$ fragmentation leads to enhanced production of
$D$ mesons at low energies. Predictions for fixed target $p+^{4}\!\textrm{He}$
collisions relevant for a fixed target LHCb experiment are discussed.
