Alfalfa growers facing water shortages can hold off on irrigating for a selected cutting and still get high yields, according to results of a three-year New Mexico State University (NMSU) study.

Leonard Lauriault, forage agronomist at NMSU’s Agricultural Science Center at Tucumcari, and Sangu Angadi, crop stress physiologist at the Agricultural Science Center at Clovis, say the goal of their irrigation termination system project is to determine which cuttings a producer can forego irrigating when water is short.

“Based on data collected so far, producers can afford to skip irrigation on one cutting during late summer or fall without experiencing a significant reduction in annual yield,” Lauriault says. “If it is known irrigation water will be short, it is best to irrigate the first three cuttings well to maximize yield.”

In warm springs, producers can significantly increase yield of the first and maybe second cuttings by beginning irrigation before typical spring green-up, whether or not irrigation water is short, according to previous Tucumcari research. “A lot of times, that can mean breaking with tradition,” Lauriault says. “For example, in areas where growers start harvesting first crop during the first week of May, they often wait until mid-April to start irrigating because that’s the way it’s always been done. If the weather is warm, though, they could benefit by starting irrigation around March 1.”

In the current project, researchers are measuring the yields of different plots of Wilson and New Mexico Common alfalfa, each with a different irrigation termination schedule. The varieties are similar, but Wilson was developed to withstand less-than-optimum soil moisture conditions. Eight irrigation treatments are being used. Furrow irrigations were applied to each of six harvests, or to various combinations of the six harvests.

New Mexico alfalfa growers typically harvest three to seven cuttings/year. By skipping one irrigation treatment at the end of the growing season, when the alfalfa does not grow as fast in preparation for winter, producers don’t risk losing yield. “They can save 6-8” of water by not irrigating that last cutting,” Lauriault says, adding that the termination strategies should be restricted to just one cutting. “Any more than that and you risk reduced yields.”

Growers considering an irrigation termination program should:

• Wait to irrigate until canopy closure – when the ground is completely shaded by alfalfa. That will limit the chance for weed seedlings to grow and survive.
  
  
• Prevent runoff by not over-irrigating. The first irrigation can be applied before spring green-up, which is a good time for growers to begin building soil-moisture profiles. Maintaining those profiles in spring and early summer will maximize yield then and establish reserves for mid- and late summer.
  
  
• Avoid trying to stretch limited water amounts over an entire season. Instead, concentrate on irrigating the first cuttings to get more yield of the crop early. “Essentially, you should water fields as though you are not facing a shortage,” says Lauriault. When the water runs out, the alfalfa’s deep roots and ability to go dormant will help it take care of itself.
  
  
• Leave 6” of stubble with leaves in the field after harvesting if alfalfa goes dormant due to drought. That will allow it to continue making its own energy.
  
  
• Irrigate alfalfa as soon as water becomes available again, since it will take the crop another cutting to recover from irrigation termination.