If one wishes to, say, use the whole food idea to affect the fortress growth;
What about taking soil fertility into account? A given patch of land might produce bundles of crops for a full year, but eveything's leached out and nothing will grow there for a time. It will make having to pay attention to crops - and getting a decent rotation of fallow and functional plots going - all the more important without actually reducing the farming output or increasing the consumption rate.
There is a difference between "player efficiency" and "dwarf efficiency". And if by default letting soul fertility degrade, and it is in effect reduce the productivity of the farming output (if no notice). So it should increase the farmers count, but not as effective and quantitative as direct approach. And wasting players' efficiency is as disruptive as increasing eating rate when building mega-projects. (perhaps not that much)
That is true... almost. It will increase the farmers count - and the number of farms - but the player efficiency need not be docked.
If you look at how the farming thing is laid out there's
already the option for a field to be left fallow for a season automatically; upon farm creation, the entire pattern can be set up and then left behind by the player. However, as it is that function has literally no use. My idea gives it some function, is already almost implemented and in latter stages of a fort, when megaprojects begin, the fortress will likely already have a decent crop rotation setup anyway.
Another farming idea (Yes, I carry on with the farming idea, since it serves as a useful base) is to limit the sheer volume of seeds that are produced. After my fortress is a year old, the whole place gets swamped by a tidal wave of seeds that I furiously begin cooking solely so that I can make room in my stockpile
for more seeds.