WWOOFing began in the early 1970s in England as a way for farmers to get weekend help. Back then, the name stood for Working Weekends on Organic Farms. It was started by a London secretary who thought city people needed a convenient way to enjoy the countryside and learn a little about the organic movement.
A trial weekend of work in Sussex quickly led to others and, eventually, chapters in other countries.
The movement was soon embraced by young adventurers as a cheap way to travel. All they had to pay was their transportation to the farm. Because they only had to work half days during their stays, they had plenty of time to enjoy themselves in a new locale.
http://www.latimes.com/news/local/la-me-wwoofing-20111125,0,1025454.story