Subsoiling hay ground

I have 2 fields of grass hay that hasn't been working up in at least 16 years,i cut hay every year on it,and this year I barely got 3 cuttings off of it,should I go in a subsoil it before hay season 2020 begins? It's hard rocky kind of ground,but i dont want to cuz a big disturbance on the top and leave a big ridge on top. Any advice is appreciated.

Subsoiling hay ground