Cumbersome.
If he needed only gas for his tractor...he'd exchange only a few wheelbarrows of grain for a few gallons of gas. Oh, but the gas isn't available from his neighbor, it has to be piped in from half a continent away.
Same for each little item the farmer needs. So...what would the farmer's reaction be in such a downturned economy? I mean, he wouldn't--as a practical matter--even bother to produce that silo full of grain.
No. The farmer would cut production down to a level to what his own family and neighbors could immediately use, or use for immediate, local area barter. Rememeber, in a broken economy there are no trains accepting money or credit to haul a silo of grain to the regional exchange.
I.e., we all starve in the cities and suburbs.
Scary, eh?
It also overlooks another pesky little problem: If the farmer is growing wheat...it's likely that ALL of his neighbors are doing...EXACTLY THE SAME THING. They'd choke on all that wheat they try to barter, because their neighbors are...uh...bartering wheat, too. The plumber and hardware store owner can only eat so much bread.
To shed all that barterable wheat, they'd need railroads. A functioning commodities exchange. A means of converting grain to a stable store of value (money).
In the event of a currency/banking collapse I plan to hasten to the local restaurant supply where I will barter for a truckload of beans, rice, lard, flour, etc. I’ll bet the owner suddenly realizes he needs more arms and ammo.
Then I will have my employees re-package it in sizes from 1/4 lb. to 10 lb.
VOILA! The new currency of the People!