Someone might have already done something like this but here is my version to help create crop rotations in a google sheet which is linked below. In the first sheet is the crop type and values. In the second sheet you can try out different rotations for farms.
Highlight the entire table in the second sheet and copy and paste it below and keep copying and pasting it for other farms. Then select a crop type using the drop down and it will fill in the fertility and grow time and colour code the fertility value. It will then give you a total fertility value for the year and also for the 3 year total. It will also show the grow time for a particular year in red if the crops chosen won’t fit in that year.
Go to the link below and then from the File menu select Make a Copy and save it to your Google Drive and then you can edit your version. I hope that this might help some people.
https://docs.google.com/spreadsheets/d/1qJS3aRgCZs9-Vnj1h8XZ7sl_KJLYJ_Mis_lDcL8ksYU/edit?usp=sharing