Let $Q=(0,T)\times��$, where $��$ is a bounded open subset of $\mathbb{R}^d$. We consider the parabolic $p$-capacity on $Q$ naturally associated with the usual $p$-Laplacian. Droniou, Porretta and Prignet have shown that if a bounded Radon measure $��$ on $Q$ is diffuse, i.e. charges no set of zero $p$-capacity, $p>1$, then it is of the form $��=f+\mbox{div}(G)+g_t$ for some $f\in L^1(Q)$, $G\in (L^{p'}(Q))^d$ and $g\in L^p(0,T;W^{1,p}_0(��)\cap L^2(��))$. We show the converse of this result: if $p>1$, then each bounded Radon measure $��$ on $Q$ admitting such a decomposition is diffuse.