Theoretically, unlimited; troops sent to other villages are supported there and recalls can put you into the negative crop.
However, if we assume positive end crop: 2450 per level 20 field, 50% bonus from mill and bakery, 150% for three oases, 25% gold advantage.
It's around 110k without the gold advantage, 120k with. Mind you, it would take a primed Teuton 40-60 days to train the troops to fill such a village with only a level 20 barracks, not to mention the massive resource cost (but if you're building level 20 fields, we can assume you have time and money).
So, do you have to worry about seeing a full-up 15 cropper? Probably not. That said, you probably don't need more than 50k troops to win most battles, since if you're rolling that, anything but a 15c is going to be completely unable to defend simply because even if they had the troops, that village will starve in minutes after their arrival.