Managing heaved alfalfa fields
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Heaving, or the pushing of plants out of the ground, has been reported in several Michigan alfalfa fields, most notably in the Central and Southern Michigan area. A photo of a field of heaved alfalfa in Central Michigan is below. Note several alfalfa plants that are heaved four inches or more that are already dead this spring.
A field of heaved alfalfa in Central Michigan.
Heaving is caused by the soil freeze-thaw cycles in late winter and
early spring. It is most commonly observed on soils with high clay and
high moisture content with poor percolation. If plants are heaved more
than an inch, the crown and taproot are exposed to late-winter weather
conditions and injury from mowing.
When heaving is observed, first dig a few plants to determine if the taproot is broken. Plants with broken taproots will likely green up and survive for a short time and then die when weather becomes warm and the soil dries. The length of time before plant death will depend on the length of taproot above the break and will range from greenup only (if tap root broke three to four inches below the soil surface) to sufficient growth for first crop (six to eight inches taproot) to growth until first dry spell (eight to 12 inches taproot).
Fields with over 1.5 inches heaving will likely have broken taproots and will also suffer significant damage from harvesting equipment. These fields should likely be terminated immediately.
Fields with one-inch or less heaving are likely to have unbroken taproots and may be salvageable for at least the current year. These fields will likely have delayed greenup. The best recommendation is to do nothing to the stands now. Do not go over the field with a roller or cultipacker in early spring to push the crowns back into the soil. This will likely to do more damage than good. Plan on harvesting these fields later than normal (25 percent bloom) and to raise cutter bar at harvest sufficiently to clear crowns. Natural settling should occur during the year and, if plants are reseated, stands should survive until next year. Stands entering the winter with elevated crowns are likely to suffer above average winter injury and kill.