ABSTRACT
The world population surpassed seven billion people in 2012. For the first time, in 2012, 50% of the world population live in urban areas, accelerating a trend of population migration from rural to urban areas. In 1900, farmers represented nearly 40% of the labor force in the USA. Today, that number has plunged to well below 2%. In the meantime, energy intensity in agriculture has steadily decreased since World War II (Davidson). Remarkably, the world has adequate food supply to feed ever-increasing world population with less farm labor force. According to the USDA Economic Research Service, the level of the USA farm output in 2009 was 170% above its level in 1948, due in part to mechanization (http:www.ers.usda.gov). It is no wonder that the US National Academy of Engineering has identified agricultural mechanization as one of the greatest engineering achievements in the 20th century (https://www.greatachievements.org/). Center to agricultural mechanization is the internal combustion engine, first introduced to farm tractors in 1902, which provides prime power for tractors, combines and other forms of farm equipment. There are few people, if any, who even remember horse-drawn carriage anymore.
