Likely it's water and arable land, yes. But you asked about food.

[There's a short pause as he thinks.]

We could equally use the griffons for flying water? Not a great deal, though. Water's heavy. Let me think on what we could do for water, other than transporting mages who can make a lot of ice which would melt rather quickly.

I've no idea if there's anything to be done about the land. Animal excrement helps, but to get a large enough quantity to make any sort of actual difference would be miserable for everyone involved.