I was inspired by all the farming talk in my thread about seasons being too short. Well that, and animal husbandry. As the title says, this is an expansion idea and not for release as I feel it's scope creep.
Farming can be so much more than sow 'n reap! Or sow, water, fertilize, weed, reap. Even if they get fancy with crop rotations and different fertilizers, any ole' peasant can do that.
Enter the Magic Peasant, or MP. That's you, the player! The MP can create Magically Modified Organisms, or MMOs, and it'll be a new processing artisan skill line on par with animal husbandry.
As with animal husbandry, there are two parts to this:
1. First is optimizing existing crops, like wheat. The MP can magically modify wheat to improve yield, increase pest resistance, and reduce water requirements and maturity periods etc. It'll be an iterative process, just like with animal husbandry, where the MP improves the wheat over time, harvest cycle after harvest cycle. At harvest time the MP can choose to harvest some for seed grains, and name the batch so any progress is saved. The MP can harvest the rest as generic wheat for crafting or selling on the market or make bread with.
In other words, you need to save some seed grain every harvest for the next crop, and then you sell the rest as regular wheat. What you gain is easier maintenance and faster time to harvest.
2. Second part is where it gets really interesting. Again, just like with animal husbandry, the MP's knowledge of MMOs is now so great they can crossbreed and create hybrid crops! These new hybrid crops can be used to create new types of food and potions by the other artisans in the game.
Or, perhaps instead of creating an entirely new type of plant, the MP can create hybrids of plants that can grow in weather they can't normally grow in. For example the MP can create a cold-resistant strain of wheat that can grow in winter by combining regular wheat and and the magic essence of a snowflower normally only found in the frosty mountains. This should probably be a lower-yield wheat, but better than nothing.
Once a new hybrid is created, it can be further improved and iterated on as per the first part above.
TL;DR: It's like animal husbandry for farming crops.