  By using the Poisson geometry, we develop a manifestly invariant and
calculation-friendly formalism for handling $UOSp(2|1)$-supersymmetric field
theories. In particular, the super-Langrangians are written solely in terms of
superfields, Poisson brackets and the moment map generating the $UOSp(2|1)$
action. As an application of this formalism, we construct the Kalb-Ramond term
for supersymmetric sigma models on the supersphere.
