PO for inventory items / Check fund

When creating a purchase order for expense items, the accounting entry for encumbrance is as follows: 

DR. Expense (Budget account) 

CR. Reserve for Encumbrance 

and we do not have issue for that 

however, the issue is when creating a purchase order for inventory items, the accounting entry for encumbrance is as follows: 

DR. Material 

CR. Reserve for Encumbrance 

The issue is that the Material account is set as an asset type not expense, and there is no Budget in this account, so we are looking for any workaround to achieve this 

Oracle EBS purchasing