Note: It doesn't matter if you do it yourself or hire a worker for this to count. However, it must be done on a field you own, hired jobs do not count for this.This is a simple achievement it just takes time. Just grab your favorite tractor, put a fertilizing unit on the back and go to town on a field you own. The bigger the fertilizer, the faster you can get this done. It is faster to rotate through the cultivating, sowing, fertilizing and harvesting on the same field so you are working on the achievements for all 4 instead of doing one group at a time.
You should get this naturally while going for these.