Strategies for Irrigating Alfalfa

Alfalfa is a water-intensive crop that faces a major challenge when irrigation restrictions are in place. However, understanding when alfalfa needs moisture the most can greatly help you schedule applications to maximize limited amounts of water.

For example, alfalfa consumes water most efficiently during its spring growth period, explains Bruce Anderson, a forage specialist with the University of Nebraska. At this growth stage, the forage crop requires only 4 to 5 acre-inches per ton of alfalfa the crop produces.

By midsummer, however, alfalfa drinks up 7 to 8 inches of moisture to produce 1 ton of forage. By fall, that water use drops back to 5 to 6 inches of water per ton of forage.

To maximize forage production with limited water, the best practice is to produce as much yield as possible during the first, or possibly second, cutting of hay, when alfalfa is the most efficient in its use of water. Following this approach might mean irrigating even before the first cutting if rainfall has been sparse during spring, Anderson explains.

What should your strategy be if you don't have access to or you are not allocated water until after the first cutting? In this case, you would want to irrigate as soon as you get water, because it will increase forage yields during the second cutting.

Strategy changes, however, in the heat of summer. This is when alfalfa's use of water is the most inefficient. At this time, avoid irrigating the crop. Then apply most of what is left of your allocation after temperatures cool down later in the year, Anderson advises.

"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," he adds.

Higher rates on fewer acres
If you must decide on spreading water lightly across all acres or using heavier rates on fewer acres, Anderson recommends applying 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," he says.

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

There are several publications that provide additional strategies to alfalfa irrigation, including these three:

• Soil-Moisture Monitoring: A Simple Method to Improve Alfalfa and Pasture Irrigation Management by the University of California, Davis.
• Key Irrigation Management Practices for Alfalfa from the University of California, Davis.
• Alfalfa Irrigation and Drought from the University of Idaho.