How does crop rotation work?

[Oedipus's Stepdad]

And why do my peasants keep planting wheat in october?

[N-xpat89]

Crop rotating is realistic (Germany did this thing called Three-Fields-Economy) - my recommendation is, build three fields each a morgen or half a morgen, set one to plant wheat (or something that fits your fertility in that place), one to wheat in the second rotation (year) and one to wheat in the 3rd year. You only would have one field yielding harvest and the other two recuperating so to say. You will ensure soil quality is maintained that way, increasing fertility of the crop.
I think the planting and harvesting cycle is bugged a little bit, but wheat and some other grains are actually planted around September and October. Winter kills off the weeds and then wheat emerges to grow around March and April.
Some varieties of grains can be sown in April I guess, but winter-wheat is and has been the main stream.