Before billions of people are starving to death though, I would imagine that as an emergency measure there would be massive shift from meat to grain production, which is multiple times more productive.

At least in the short term, if we get long term issues of that scale, things might be different.

Also when it becomes a matter of survival, market economics stop to matter. Then it becomes a question if a state can afford to close the financing gap or not. The EU is already subsidising agriculture for productiveness to secure regional food production for example. The mechanisms are already there, they just would have to be strengthened.

Diesel demand is currently falling in Europe as diesel cars are becoming obsolete. If saving fuel for agriculture becomes a priority, just push harder for EV transition.

Lastly, ammoniac can be produced from air, while that requires s lot of energy that does not have to come from fossil sources. Also, just shit down all those useless ai data centers during a state of energency to secure energy for fertiliser production.