Irrigating Alfalfa When Water Is Limited

By Bruce Anderson

Extension Forage Specialist

Figure 1. Alfalfa field near Concord in northeast Nebraska

Alfalfa can use a lot of water. With less irrigation water available, you may not be able to fully irrigate all your alfalfa acres.  So how do you make best use of the water available?

Alfalfa uses water most efficiently during spring growth, requiring only four to five acre inches per ton of hay.  By mid-summer, though, it takes seven or eight inches to produce the same ton of hay. By fall, that may drop back to 5 or 6 inches per ton.

To maximize yield with limited water, produce as much yield as possible during the first cutting or two, when water use efficiency is highest.  This could mean irrigating even before first cutting if rainfall is sparse during spring.

What if you won't receive any water until after first cutting?  Irrigate as soon as you get water if it will increase yield enough during second cutting.  Avoid irrigating alfalfa in the heat of summer when water use efficiency is reduced, and then apply most of what is left after temperatures cool down later this year.  You might want to modify timing a little, though, to avoid having hay ready to cut near the end of September while it is winterizing.

If you must decide on spreading water lightly across all acres or using heavier rates on fewer acres, I recommend heavier rates on fewer acres.  The first couple inches you apply just keep plants green without growing.  Once this maintenance moisture is met, the rest of the irrigation produces growth.

Whatever you decide, be sure to prioritize your best land for irrigation because that's where plants will respond best to extra water.

Source:unl.edu