  We consider the construction of the algebraic part of D-branes tree-level
effective action from Berkovits open superstring field theory. Applying this
construction to the quartic potential of massless fields carrying a specific
worldsheet charge, we show that the full contribution to the potential
localizes at the boundary of moduli space, reducing to elementary two-point
functions. As examples of this general mechanism, we show how the Yang-Mills
quartic potential and the instanton effective action of a $Dp/D(p-4)$ system
are reproduced
