Sorry for the late reply.
You can buy the Agriculture Skill from a Succubus on the second floor of the Goblin Brothel on Saturdays. You can also very rarely find it in Chests as a Book. Another way is to Enslave the Student NPC and donate him to a Goblin Household, then he will teach it to you for a price.
To Break the Curse:
1) Capture a Student NPC (you have to use Invisibility Potion first and hit him over the head while carrying a Rope in your Inventory. Then bring him to Saffron.
OR
2)Find a Priest NPC and buy a Remove Curse Scroll from him.
These NPCs have a ~30% chance to spawn once a day per map in a random location, though they are more likely to spawn near roads. They wont spawn at Night and if you leave the map they despawn.