Later in the game when I have a few fields established already, I will add one that's either spring wheat and rye, or autumn wheat and cabbage. I tend to compost my cabbage for rot which I can then make into fertiliser. It's all situational - if I need more fertiliser I'll go with cabbage, if I've got that covered (say with a pig farm) then I'll go with more grains.
Later in the game when I have a few fields established already, I will add one that's either spring wheat and rye, or autumn wheat and cabbage. I tend to compost my cabbage for rot which I can then make into fertiliser.
It's all situational - if I need more fertiliser I'll go with cabbage, if I've got that covered (say with a pig farm) then I'll go with more grains.