If you check the paper, it doesn't say "plowing" anywhere. Just tilling. And these are the parameters:

> Tillage had been applied at three depths commonly used in farming—no tillage, 10 cm, and 25 cm—while compaction had been imposed using two tire pressure levels—70 kPa for both front and rear tires, and 120 kPa for front and 150 kPa for rear tires.