If you visit a neighbor or friends farm you are given the option to help out around the farm. This can be scaring off pets or raking leaves or many other things. If you do this you will be rewarded with some coins and XP. IF that person has crops which are still growing(IE can't be ready to harvest yet.) you will be given the option of fertilizing up to 5 crops. By doing so their crops will grow bigger than normal and they will also get XP when they harvest them. You'll get additional points towards a ribbon for fertilizing.