This is so because legal tender laws allow debtors to effectively abrogate private currency debt contracts at will by offering Federal Reserve notes in lieu of what was specified.
The local currency could be devalued based on an agreed upon schedule or allowed to float within a specified range in order to restore competitiveness and economic growth in the local market.
Each Terra can be turned in for the specified share of the basket of commodities, which would be held as 100% backing of the currency, under contract with producers of those commodities who are partners in the financial institution issuing the Terras.