The Bug:

Sculk sensors are not activated upon farmland hydrating or dehydrating.

Steps to Reproduce:

• Hydrate or dehydrate farmland.
  →  Notice how the sculk sensor does not activate upon doing either of these things.

Additional Information:

Quote from the 20w49a Changelog, "A vibration is anything that causes physical motion". I would definitely consider this as physical motion, as these blocks are changing state.