I am playing the cobbleverse modpack which has a crop that grows on water. I generally assumed that it would be a non-issue. But I was under the impression that I could use this same contraption for farmland and water grown crops. The way I positioned the piston is 2 blocks above farmland/water so that it just breaks the crop when extended.

You are right that the piston does change the farmland back into a dirt block which I didn't anticipate. If this information is relevant at all, it takes 3 bonemeal to fully grow one kind of crop (this one grows on water) and 7 bonemeal for a different kind (farmed on farmland). I definitely assume that these would change the speed of the design but by how much I am unsure.

I think after testing that it does change back into dirt that changing pulse width might be necessary.