Cashcropper allows you to compare the net profitability and fertility requirements for different crop rotations within a given field. This app is powered by over 30 years of data on crop yield responses to different rotations from trials conducted by the University of Guelph. The app uses default yield values provided by crop insurance records in Ontario and uses the Ontario Ministry of Agriculture, Food and Rural Affairs cost of production defaults as a starting point for the user. The user can change any of these values to better reflect their operation.
Although the yield responses used in this app are based on an extensive, long term database, there are no guarantees. But if you're using this app, you're likely a farmer and already know that the only guarantee in producing a crop is that you're at the mercy of mother nature.