Alfalfa is one of the most important forage crops grown for hay in the world today, because with ample water, it has the ability to produce high yields of very good quality feed that is high in protein. It is well adapted to a wide range of soils, is relatively drought-tolerant, but also responds well to Irrigation.
Alfalfa is a high water use crop requiring about 4 to 6 inches of water for each ton (11 to 17 cm per tonne) of dry hay produced. If the water is available, alfalfa will use more water than most other crops because of its long growing season. In many alfalfa growing areas, water is the most limiting factor.
Irrigating alfalfa is different from irrigating annual grain crops because the objective is to
produce a high yield of forage and not grain. Some important differences include:
• Alfalfa is a perennial crop with a potentially deep root system that can use water deep within the soil profile.
• Multiple harvests prevent irrigation for about 7 to 10 days per growing cycle.
• Frequent heavy equipment traffic across an alfalfa field causes soil compaction and often forms a crust on the soil surface. This crust can result in reduced soil water infiltration rates as stands age resulting in an increased potential of Irrigation water runoff.
• Water-logged soils from over-irrigation or too much rain can quickly injure alfalfa plants and encourage weed invasions, especially right after harvest.
Water use efficiency is the greatest during cool to moderate temperatures, especially during spring.
Alfalfa is a deep rooted perennial crop that can use water from deep in a soil profile. Alfalfa roots can penetrate 8 to 12 feet (2.4 to 4 m) deep in a well-drained soil. However, irrigated alfalfa will obtain 75 to 90% of its water from the upper 4 feet (1.2 m) of soil. Drought stress will cause plant growth to simply slow down or even stop and go dormant if the stress is severe enough. A lack of water at any growth stage will lower the yield, cause the forage quality to peak in fewer days after harvest, and become overly mature faster than under normal conditions.
Well watered alfalfa will have a light green color which will turn to a darker green color as water stress develops, followed by plant wilting. Wilting will usually start as the soil in the active root zone dries to about 25 to 30% of plant available water. Irrigation should be completed before wilting begins to prevent yield loss. Ideally, the soil water content in the effective root zone should be kept between 50 to 90% to achieve optimum yields.
• Focus on filling the soil profile to a depth of 6 to 8 feet (2 to 2.5 m) with rain and irrigation during the fall and spring periods. The plants can use this water during hot, dry times of the summer when it is very difficult to provide enough water with the irrigation system.
Light and frequent irrigation is best right after planting to establish the alfalfa stand. However, following stand establishment, less frequent Irrigation of 1 inch (25 mm) or more should be applied. The larger the application amount (up to 3 inches or 75 mm), the better it is at encouraging a good deep root system. Preventing runoff is a must and will be the limiting factor on the amount of water that can be applied with each pass of the pivot. Some producers like to make the first irrigation after harvest fairly light (0.5 inches, 13 mm), so the entire field can be watered quickly to get the growth off to a good start and then start the deeper watering.
growth has started to prevent weeds from germinating .However, on lower water-holding capacity soils and on lower capacity irrigation systems, watering may need to continue until two or three days before harvest and start again as soon as the hay is removed from the field.
Irrigation management after harvest needs to be a balance between the facts that if the soil is too dry, regrowth will be slowed and that if the soil is too wet, it will promote weed germination and could damage the alfalfa plants. With this in mind, a good irrigation philosophy is to focus on providing water for the next cutting rather than for the current growth. This strategy should provide adequate water to get regrowth started.
Source: Irmak, S., D.R. Hay, B.E. Anderson, W.L. Kranz,
and C.D. Yonts. 2007. Irrigation Management and
Crop Characteristics of Alfalfa. NebGuide G1778.
University of Nebraska-Lincoln Extension