Healthy roots (left) and injured roots (right).
Healthy roots (left) and injured roots (right).

It’s time to head to the field and see how your alfalfa fared through the winter. Often, there will be signs of injury or winterkill but expect it to be spotty in areas with low soil pH, potassium and sulfur, and in older stands.

“It’s also important to look for injury without winterkill and plan for those areas to have a reduced yield,” said Dan Undersander, forage agronomist, University of Wisconsin Extension. “It’s best to know both scenarios early, so you can make management decisions accordingly.”

Tips to Identify Injured or Killed Alfalfa

  • Check visually for slow or no “green up” in your fields. In the fall, the roots story energy that the plant can utilize during the winter. Into the spring, it helps with growth of shoots and to form crown buds. Injury can either destroy the roots and crowns, or some crown buds may survive and slowly regrow. Regrowth of crown buds may only be a few per plant, and they could be stunted or chlorotic (yellow). A healthy stand should have 55 stems per square foot.
  • Uneven regrowth.  Damage to some crown buds during winter will create uneven regrowth. Surviving buds will grow, and new crown buds will regenerate but will be 3" to 4" shorter. Expect some shoots to die in plant-damaged areas.
  • Root damage.  The best way to assess root damage is to dig a few plants 4" to 6" deep and look at the condition of the taproot. If roots are firm and white, they are healthy. Damaged roots are yellowish gray  with a spongy dehydrated look and feel.  If you find damage, expect roots to turn diseased and shift to a dark brown color. They won’t be able to grow and maintain crown buds.  

To estimate future yield potential in your alfalfa field, assess stem densities per square foot using the following guidelines:

  • Greater than 55 stems—density should not limit yield
  • Between 40 and 55 stems—expect some yield losses, but fields might still offer enough yield depending on your needs
  • Fewer than 40 stems—this is a poor stand and yield losses will be significant

Thin stand                                                Adequate stand

Photo courtesy of Dan Undersander, University of Wisconsin

Stand yield and injury will ultimately affect silage quality and yield. Follow these best management practices to make the most out of your silage crop:

  • Timing is critical to alfalfa harvest. Cut at late-bud stage of maturity or 28" height (whichever comes first) to optimize quality of low neutral detergent fiber, low lignin and high fiber digestibility.
  • Mow and lay alfalfa in a wide swath to allow it to dry quickly. Mowing with a roller conditioner can also minimize leaf loss.
  • Ensile at 65% moisture, harvesting when alfalfa is wetter to avoid leaf loss.
  • Pack fast but densely to exclude air from the forage. Packing density should be 45 lb. per cubic foot.
  • Inoculate silage to prevent clostridial fermentation and enhance aerobic stability.
  • After filling bunkers and piles, cover silage immediately with two-layer plastic to limit exposure to the air.
  • Avoid a “fall slump” in milk production by allowing silage time to complete the fermentation process. 
  • When making or working with silage, don’t forget about safety. Consider danger points and review them with your staff and family.