Look here:http://www.the-nextlevel.com/tropico/cafe/index.php?topic=9134.msg185787#msg1857874) Crops. Q
One of the most frustrating things in a game is to develop a dependency on a single cash crop, only to notice later that the land devoted to the farms has turned orange, indicating that it is unsuitable for that crop. Is crop rotation necessary, or is the change purely climatic? Can you anticipate changes by using the info overlays for soil and rain? A Rotating crops has no impact. It's purely climate related, based on rainfall. The initial values for crop suitability are are based on the game running an internal weather model for 80 years at game start, and averaging the results. Of course, it's a long-term average, and there are short-term fluctuations. Steinmeyer: "I usually just accept that there will be good and bad harvests, based on the rainfall... I don't typically adjust my crop patterns too much after I've built a farm."
Steinmeyer is/was the principal developer. Newer information indicates that pollution radiated from buildings and people permanently changes the soil quality. To the extent that farms and ranches radiate some pollution, there is a crude simuluation of crop's depletion of the soil. Simply, for gameplay in an 80 year time-frame is too mico; and besides there is no recovery.