When furrow irrigating, water flows in evenly spaced furrows or corrugates that are typically 0.1–0.3 m wide on fields with slopes of 0.1–3%. Water commonly flows in furrows for 12–24 hours during irrigation, but shorter or longer durations may be used depending on furrow length, soil properties, and water management considerations. Inflow rates for individual furrows can vary from about 10 to 100 L min-1 , again depending on soil, slope, field length and management considerations. Ideally, water should advance across the field in about 25% of the total irrigation time to uniformly irrigate the field. Since soil erosion increases as field slope and inflow rate increase, the flow rate must be carefully managed on fields with steeper slopes (>1%). Low inflow rates and long irrigation durations may be needed to apply the desired amount of water during irrigation on soils with low infiltration rate.
Conversely, higher inflow rates are often needed on fields with low slopes and/or high infiltration rate soils in order for the water to flow across the field and uniformly irrigate the upper and lower portions of the field. Inflow to irrigation furrows may be supplied from gated pipe or ditches (earthen or concrete). Siphon tubes are frequently used to convey and regulate water flow from ditches to individual furrows. By creating a siphon, water flows through the tube, over the ditch bank, and into the furrow as long as the tube outlet is lower than the water elevation in the ditch. Furrow inflow rate is controlled by tube diameter and the elevation difference between the ditch water level and tube outlet. Gated pipe distributes water to furrows through evenly spaced outlets on the pipe. Furrow inflow rate is controlled by outlet opening and water pressure within the gated pipe. With earthen ditches, water flows through a breach or other opening in the ditch bank to individual furrows or a smaller feed ditch that distributes water to several furrows.
It is much more difficult to regulate flow through a breach in an earthen ditch than through siphon tubes or pipe gates. Furrow irrigation requires lower capital investment, less technical knowledge and greater labor than most other irrigation systems. Fields can be irrigated without leveling or grading because the water flows in furrows. Furrow irrigation is not well suited to automation because water flow rate must be adjusted for each furrow for each irrigation.