Crop Rotation Yield Benefits

Yield should be increased and growing time should be shortened if the player rotates the crop on a field. 
Just like in real life rotating the crop should have beneficial effects on the yield.
It also teaches the importance of sustainability and some basics of organic farming.

Example:
If full grown wheat on a block is harvested, planting a different crop on the same block like for example beetroot should have a slight boost on its growth rate and should give slightly more yield when harvested. After that if the player plants beetroot on the same block again the benefits should go away. Changing to a different crop like back to wheat or anything else should keep the benefits going.

This keeps farming interesting and gives the player something to do, while also teaching.