  It is proved that any Rota---Baxter operator of zero weight on Jordan algebra
of a nondegenerate bilinear symmetric form is nilpotent of index less or equal
three. We state exact value of nilpotency index on simple Jordan algebra of
Clifford type over fields $\mathbb{R}$, $\mathbb{C}$, and $\mathbb{Z}_p$. For
$\mathbb{Z}_p$, we essentially use the results from number theory concerned
quadratic residues and Chevalley---Warning theorem.
