* Bonuses of the same Special resource type cannot be accumulated. If there are 2 bonuses of the same type, only the bigger one is accounted. The same bonus granted by two different special resource terrains are accumulated.
Example: If you have 2 colonies on rich gold field, you will have 10% gold income bonus. If you have 1 colony on rich wheat field and 1 on rich rice field, you will have 20% farm effect bonus.
RTFM