Sure, I'll bite...kinda stupid of me since I really don't know the full extent of the mechanics but hey-ho
Tier 1: You've really gotten better at this tilling business and can prepare the soils to become the perfect home for your seeds. (+50% yield from crops planted in tilled dirt.)
Tier 2: Your knowledge of seeds and planting of crops are next to none and as such you can stretch your resources even further. (Double the yield when receiving seeds.)
Tier 3: One harvest what one sows, you on the other hand seem to harvest more than you sow. (Add an extra harvest cycle with half the yield of the first one, rounded down ... if possible with the current mechanics)
Tier 4: Water is the source of all life, you discovered a way to make your plants thrive even further by building an irrigation system. (A new model of a barrel with some feet on it, two blocks tall, with a piece of pipe with a valve sticking out of it and angles 90 degrees and into the ground. Fill with bucket of water and use the same system as refilling vehicles with fuel. Consumption depends on connected tilled earth slots. This irrigates connected tilled earth slots and decreases growth time by 50% and yield by 50%)
Tier 5: You've discovered that fertilizers will really put some sprout into your...well...sprouts. (New recipes opens up in the Chemical Station adding a way to create some liquid fertilizer that can then be mixed with the water bucket and create fertilized water to put into the irrigation barrel. Increases yield by 100%)
...just of the top of my head here ... I am sure I am swinging a miss but hey, at least I am swinging