Monohan wrote:What should be the field to compost bin ratio?
That's going to depend on how you raise them. If you're pushing speed on something like low end cereals just to keep stocks of flour up, then you'll need more.
Every bin produces one humus every two hours, which means 12 humus a day per bin. Each field requires 5 initially and then 2 once your upkeep is down. If you're shooting for 150% speed then fields take around two days to grow for cereal and cabbage, or 2 days and 16 hours for cotton and pumpkins. At base speed it's 3 days and 4 days. Which means if you keep the bins producing non-stop you're able to keep up with 18 cereal/cabbage fields or 24 cotton/pumpkin fields per bin. Of course this doesn't consider any extra humus you use for sake of plenty or influence gains once planted.
Of the fields I plan to have, I currently have twelve, and I use three bins, but they're regularly nearly full, even using humus for fertilizer. You could probably get away with one bin per eight or ten fields pretty comfortably.