Hi Ryan
I recommend you to use separate document type for the purchase order that have material code involved. Then you can create you screen layout copying existing layout NBF, Keep it same as your new document type that you are going to create
1. Mark Material code Mandatory and also mark short text as display under Basic, Item text.
2. Now create the new document type and assign the screen layout that you created.
Now You have display for item short text and even made material code mandatory. It is recommendation.
Thanks,
Jagdeep