The small square balers baling at low speed don't take much power at all for the baling. The power need increase with ground speed increases, larger windrows, towing a hay rake either for a kicker baler or flat stacking, then start throwing in some hills and it just keeps going up. When I starting having to stack bales on a flat wagon my father was baling with a WD Allis Chalmers, then he got the 400 Farmall just to make me work harder and to handle bigger loads on steeper ground. Then the Farmall 560 and the first baler with the thrower (belt). All of a sudden we had to have 3 wagons for him to bale with so we could haul and unload into the mow and stack without him having to stop. At that time we were doing 10,000 to 18,000 bales a year.
Times do change now with beef cows my nephew just does a few hundred small square and several hundred big rounds.