In surface irrigation, water is applied by allowing it to flow over the surface by gravity or through drip valves (a process called trickle or drip irrigation). The common gravity systems are flood and furrow. Flood systems require relatively flat land and the water is distributed in level borders or contoured levees. Land for furrow irrigation can have a small slope. For level borders and contoured levees, the water usually is delivered by surface ditch. Ditches can deliver water for furrows, but a gated pipe or a siphon tube is also used. As a general rule, gravity systems require more labor than sprinkler systems to maintain the ditches and the dikes, move the gated pipe, and control the flow of the water.
In trickle irrigation, drip valves or emitters are located along a line at uniform spacing or at each large plant. These systems have high application efficiency because a very small amount of water is applied and it is applied directly to the plant.
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