  We study Neumann coefficients of the various vertices in the Witten's open
string field theory (SFT). We show that they are not independent, but satisfy
an infinite set of algebraic relations. These relations are identified as
so-called Hirota identities. Therefore, Neumann coefficients are equal to the
second derivatives of tau-function of dispersionless Toda Lattice hierarchy
(this tau-function is just the partition sum of normal matrix model). As a
result, certain two-vertices of SFT are identified with the boundary states,
corresponding to boundary conditions on an arbitrary curve. Such two-vertices
can be obtained by the contraction of special surface states with Witten's
three vertex. We analyze a class of SFT surface states,which give rise to
boundary states under this procedure. We conjecture that these special states
can be considered as describing D-branes and other non-perturbative objects as
"solitons" in SFT. We consider some explicit examples, one of them is a surface
states corresponding to orientifold.
