I spent a lot of time with my maternal grandfather during my growing up years. He never owned a farm but share cropped all his life, always with horses and/or mules. I once asked him how much ground he could plow with a pair of mules in a day. His answer was that, with a pair of "long stepping" mules and a 12" walk behind plow, if you started early and stayed late, you could cover about 2 acres on a good day.