The United States of America is recognized as one of the largest producers of food and fiber in the world. The application of machines to the agricultural production has been a major factor of the outstanding developments in American agriculture during the past century. The continuous improvement of farm machinery contributed to the increase of the United States agricultural production while releasing millions of agricultural workers to other industries. Today the farm population of the United States accounts for only 3.8% of the total population (USDA Agricultural Statistics, 1978).