It’s that the time of the year when college basketball aficionados anticipate their favorite team’s run through the bracket, or at least the team they’ve got picked to win it all. Anticipation is all part of the fun because everyone thinks they’ll be a winner at this point.
This is also a time when Northern alfalfa growers hope and pray for the greening of their alfalfa fields. Here, the stakes are a little higher than on the basketball court.
“Energy reserves and cold resistance of winterhardy alfalfa varieties are normally greatest in December to January and then slowly decrease until March when dormancy is broken as soil temperatures climb,” explains Craig Sheaffer, forage extension specialist with the University of Minnesota. “Several days of soil temperatures of 41°F and above are required for dormancy to break. Once broken, overwintering crown buds that formed become vegetative and elongate, and we typically begin to see regrowth during April,” he adds.
Air temperatures across much of the northern U.S. have been well above normal over the past month or more. For this reason, Sheaffer believes that alfalfa will likely break dormancy early and new shoots will be visible soon, if not already. Still, the forage specialist believes that most alfalfa in his state is in pretty good shape because:
1. Alfalfa had a long period last fall to build energy reserves as temperatures were above normal through November.
2. Dry soil during the fall and winter in major producing regions reduced free water in the plant and enhanced winterhardiness.
3. Soil temperature in the top 2 to 4 inches remained from 20°F to 40°F for most of the winter. That’s still cold enough to keep alfalfa from breaking dormancy.
Not out of the woods yet
“If warming air temperature trends continue and alfalfa breaks dormancy, there is a risk of significant frost damage to new shoots if minimum air temperatures of 24°F or less occur,” Sheaffer notes. “If this happens, then new regrowth would have to come from newly formed crown buds.”
Plant heaving of the crown and roots is another risk associated with fluctuating temperatures during this time of year. Sheaffer explains that heaving is a volumetric expansion of the soil caused by the segregation and expansion of frozen water (ice) in the soil. Heaving injury results in breaking of the tap root, shearing of lateral roots, and exposure of crowns above ground.
Sheaffer feels there are two important previously implemented practices that will help reduce the risk of injury this spring. These were leaving adequate regrowth last fall and variety selection.
“Alfalfa stems and leaves remaining in the field are valuable to buffer the soil against winter soil warmup when air temperatures rise,” the forage specialist asserts. “In recent measurements we have taken, soil temperatures under unharvested stubble were 5°F less than bare soil where fall harvests occurred. This is beneficial in delaying the premature breaking of dormancy.”
Alfalfa varieties are characterized for winterhardiness, fall dormancy, and disease resistance. Sheaffer recommends that varieties grown in Minnesota have a winterhardiness rating of 1 or 2. He also thinks that fall dormancy reaction may be especially important this year in protecting alfalfa from late-season winterkill because varieties with greater fall dormancy are slower to emerge from dormancy in late winter than less dormant varieties. Having a fall dormancy rating of 2 to 4 will be beneficial in a spring such as this one.
