Ploughing with horses at the Sussex Ploughing Championships -  

Mechanization brought tractors to the fields, and horses were the main source of power used to plough furrows in preparation for planting. In a nod to their strength, tractors today are categorized according to their "horsepower" -- or how many horses it would take to accomplish the same power output.
The agricultural legacy of plough horses is preserved via annual ploughing matches in many countries. Draft horse enthusiasts compete in categories including antique plough, walking plough and two- and three-horse sulky -- that's a plough with a cart behind it so the ploughman can ride. Competitors are judged on the straightness and quality of their plough rows, quantity of ground ploughed and time.