If there is still flat land and a pond or something, I suggest you build an ecological chain farm.

Plant cash crops and some plant crops that livestock can eat on the mountain, and then raise pigs and pigs to find their own meals once a day (you need someone to watch them, or you will lose money if you run away). Fish will eat the excrement of ducks and fish in fish ponds.

Specifically, look for information about ecological chain farms. This method can mainly save the cost of raising crops and chemical fertilizers.