Do you know how big a bushel actually is? It's quite a bit for one person to carry, even if it's divided up into a few different bags and sacks slung about his person.
A bushel is 8 gallons of dry goods, or roughly 32 liters. A bushel of wheat, for example, weighs 27 kilos, or 60 pounds.
We can't expect a single soldier to carry more than a bushel, really, and even that is probably a stretch. Even then, that means a medium sized army could remove 500 bushels from a single region, which is certainly enough to cause problems in most cities.
