I have an really old "Ferguson" 2 bottom plow, I think a 16", and it takes a minimum of 50hp to pull it through my hard clay soil. I can tell you from experience that a 30 hp tractor will not come close to beginning to pull my plow, unless you only plan to plow about 4 or 5" deep. My plow is a beast, does a great job, but requires quite a bit of hp to plow a good 12 inches or more. 25 hp would never move it in my soil. Heck, 30 hp would't. I have to add weight and my FEL on the front for more weight and my 50 hp doesn't pull it any too easy. I'd call 50 hp about "adequate" for my plow.