Management of drought-stressed alfalfa

By Nathan Winter and Dan Martens
University of Minnesota Extension

During the 2006 dry spell, Peter Jeranyama, South Dakota state forage specialist, described the affects of drought on alfalfa this way: Alfalfa can go dormant during extended dry periods, and is one of the few crops that can recover when adequate precipitation occurs. It is vitally important to maintain a viable plant root system (must be white, moist and pliable) to enable alfalfa plant to survive. Under drought conditions, the alfalfa plant reduces stem number, stem elongation and yield while increasing leaf to stem ratio. Forage quality is usually higher in drought stressed alfalfa compared with normal conditions. Photosynthesis is maintained during the early phase of drought but slows as the drought continues and as the stomata close. Nitrogen fixation and nodule formation is reduced but more nutrients accumulate in the roots compared to the foliage. In new seedings, root growth is affected more than shoot growth.

Jeranyama says cutting management is a primary factor for increasing stand persistence during drought periods. Genetics and preconditioning of the stand can be factors in drought periods. Cutting decisions are best based on the plant’s maturity stage and economic cutting heights. Established alfalfa stands, as well as new seedings, should be harvested only if there is enough forage to economically justify harvesting. If enough alfalfa is present to justify harvesting, the quality of harvested alfalfa should be excellent. Alfalfa should be mowed or clipped after the drought is broken to stimulate regrowth. This is particularly important if the alfalfa is blooming or near blooming, as clipping at this growth stage will encourage new crown buds to send out new shoots for regrowth.

Wisconsin Extension Forage Specialist Dan Undersander offers the following recommendations when the alfalfa has been stunted and is flowering: If stand is over 10 inches tall and flowering, harvest. If stand is 10 inches or less, leave and let new growth come through (even if short growth is flowering). Mowing will not increase regrowth. Sunlight coming through the canopy into the crown areas is a key factor in stimulating new growth. Make sure that soil fertility is at optimum levels.

Jeranyama says it is important to maintain enough leaf material for the stressed plant to continue photosynthesis and root growth. Cutting during drought is similar to dormancy management. Ideally if crop is cut during drought, maintain at least 6 to 8 inches of top growth. This height allows continued root and plant functioning, so that the alfalfa can persist through the fall and winter. Although forage quality is higher at the pre-bud stage, allow the alfalfa to reach at least 10 percent bloom stage before cutting when under drought stress. At flowering, alfalfa is better able to handle dry weather and cutting stress.

If stands have entered the dormancy stage and top growth does not extend beyond the original 6 to 8 inches left from the previous cutting, avoid cutting to allow the plants to survive the drought conditions.

Call the McLeod County Extension at (320) 587-0770 or Meeker County Extension at (320) 693-5275 for more information.

(Nathan Winter is an agricultural educator for McLeod and Meeker counties with University of Minnesota Regional Extension in Hutchinson. Dan Martens is an agricultural educator for Stearns, Benton and Morrison counties with the University of Minnesota Extension.)