Water use is high in alfalfa ...

Water use is high in alfalfa because it has a long growing season, a deep root system, and a dense canopy of vegetation. The amount of water needed for alfalfa production is a function of temperature, wind, humidity, and the amount and intensity of light. The irrigation requirement for alfalfa is determined by rainfall and the water holding capacity of the soils growing the crop. Commonly cited ranges in water requirements for alfalfa are 20 to 46 inches of water per season, depending on climate, elevation, growing season, number of cuttings, latitude, and fall dormancy rating of the alfalfa variety. Not much water is exported with alfalfa hay. Potential irrigated alfalfa hay yield at elevations near 4000 feet is about 7.5 tons/acre. Hay harvested at 12% moisture removes 240 lbs water/ton hay, or 1,800 lbs/acre for a normal crop of alfalfa hay per year. Evapotranspiration (ET) is the primary use of water by alfalfa and averages about 36 inches/year (900 mm) at Kimberly. The ET at peak periods of 0.4 inches/day (10 mm/day) can reach 4080 tons of water per acre and 45 tons per acre per day. As shown in Figure 1, adequate center pivot irrigation system capacity is critical for maintaining acceptable soil moisture levels (and yield potential) later in the season. Systems designed and operated to apply less  than 7 gallons per minute are not able to match ET and must rely on soil water bank to supply the deficit.