  We study a (2+1)-dimensional system that can be viewed as an infinite number
of O(3) sigma-fields coupled by a nearest-neighbour Heisenberg-like
interaction. We reduce the field equations of this model to an integrable
system that is closely related to the two-dimensional relativistic Toda chain
and the Ablowitz-Ladik equations. Using this reduction we obtain the
dark-soliton solutions of our model.
