The USGS Water Science School
Probably one of the oldest methods of irrigating fields is surface irrigation (also known as flood or furrow irrigation), where farmers flow water down small trenches running through their crops. Humans' first invention after learning how to grow plants from seeds was probably a bucket. Ancient people must have been strong from having to haul buckets full of water to pour on their first plants. For most of human history, people did not have mechanized spray irrigation systems to apply water to crop fields. It was more like, "Hey, Big Guy, take this reed bucket and go down to the river and fill 'er up."
Surface irrigation is still used today throughout the world,especially in less-developed areas where mechanical techniques are not available. In fact, in the United States in 2000, about 29.4 million acres were irrigated by flood irrigation as compared to about 28.3 million acres irrigated by spray irrigation. Flood irrigation is not the most efficient irrigation method, but it is cheap and low-tech. On the one hand, less water is lost to evaporation than in spray irrigation, but on the other hand, more water can be lost from runoff at the edges of the fields.
Here are some more-efficient surface-irrigation techniques that farmers use:
Surface irrigation water use in the United States
Irrigation is one of the major uses of water throughout the world. In the United States in year 2000, irrigation withdrawals were an estimated 137,000 million gallons per day (Mgal/d), or 153,000 thousand acre-feet per year. About 61,900 thousand acres were irrigated in 2000. Of this total acreage, about 28,300 thousand acres with microirrigation systems. The average application rate was 2.48 acre-feet per acre for the United States.
Irrigation water use | Irrigation techniques | Irrigation methods
Irrigation use, 2000: Data table | Map
Irrigation methods: Spray | Flood | Drip | Low-energy