Does zakat become obligatory upon the debtor, especially if his debt is an usurious loan?

A person in debt is not obligated to pay Zakat on hidden wealth (gold, silver, money, and trade goods). However, Zakat is obligatory on apparent wealth (crops, fruits, and livestock). Money borrowed through usury is ill-gotten wealth that must be disposed of by returning it to its owner or returning its equivalent. There is no Zakat on it for the borrower; rather, it is obligatory on its owner.