May 2, 2008 

Alfalfa can use a lot of water, which may be a problem this year in areas where water is limited and reduced irrigation may become a reality.

Alfalfa uses water most efficiently during spring growth, requiring only 4-5 inches per ton of hay. By mid-summer, though, it takes 7-8 inches to produce the same ton of hay. By fall, that may drop again to 5-6 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.

If you don't receive any water until after first cutting, irrigate as soon as you get water if it will increase yield enough. Avoid irrigating alfalfa in the heat of summer when the plant doesn't use water efficiently. Wait to apply most of what is left after temperatures cool down. 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 need to decide between spreading water lightly across all acres or using heavier rates on fewer acres, I recommend heavier rates on fewer acres. It takes a couple inches just to keep plants green without growing. Once maintenance moisture is met, the rest produces growth.

Whatever you decide, be sure to use limited water on your best land, where plants will respond best to the challenge.

Bruce Anderson
Extension Forage Specialist