This is more of a quality-of-life improvement, but something that to me would greatly improve gameplay.
1: Add the ability to copy/paste rotations between farms.
2: Add a button to shuffle crop rotations more easily. This goes in tandem with #1, so you just need to copy in the rotation and hit the shuffle button once to push it forward by one year.
3: Add the ability to delete a single year as well as the entire rotation with just one click. It can become a tedious task to have to click 6-10 times for each field if you have to clear it completely.
4: Create rotation presets that are game-wide. I have different crop rotations for early, mid and late game, so combined with ideas in earlier points, this could also vastly improve gameplay, especially if you have farms that get hit by diseases on higher difficulty playthroughs.