The original idea is Ben Franklin's.
http://webexhibits.org/daylightsaving/franklin3.html
But in the modern world it had nothing to do with the farmers, the reason we use it was from WWI. By moving the clock ahead one hour, it was found that you could save the fuel needed to produce electricity, by using the extra daylight.
The US started using it in 1918 and ended in 1919.
FDR again used it during WWII from 1942 until 1945, for the same reasons.
And for those of us old enough to remember, Nixon had the Emergency Daylight Saving Time Energy Conservatoin Act of 1973. It put the country on year around DST from Jan 1974 until April 1975.
http://webexhibits.org/daylightsaving/e.html