Does usury apply to exchanging a borrowed kilogram of rice for another kilogram of rice after a period, if the types differ in quality but are equal in value?

It is permissible to give a loan (qard) in ribawi (interest-bearing) and non-ribawi currencies. The conditions of immediate possession (taqabud) and equivalence (mithliyah) that apply to ribawi transactions in sale do not apply to loans. However, it is forbidden to stipulate an increase over the amount loaned in a qard, as this constitutes usury (riba). If the increase comes from the borrower himself, it is permissible and even desirable, considered a form of good repayment (husn al-qada'). This applies whether the increase is in quantity or quality, and it does not fall under the prohibited riba because the prohibition applies only to what is stipulated in the loan contract.