March 12, 1992

Revised Apr, 2002

Heaving in Alfalfa Fields

Dan Undersander

University of Wisconsin

Heaving is likely to be a problem in some alfalfa stands in eastern Wisconsin this spring. Heaving occurs on heavy soils that have high moisture contents. Repeated freezing and thawing causes soil expansion and contraction that pushes the tap-rooted plants out of the soil.

Where 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 while and then die. They will also tend to have reduced yield when moisture is short over summer. 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 broken three to four inches below the soil surface) to sufficient growth harvesting first crop (six to 8 inches) to growth until first dry spell (8 to 12 inches).

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 heaving 1 inch or less 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% 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 winterkill.

Heaving in future years can be minimized by having good internal and surface drainage. Tiling may reduce heaving problems depending on the depth of the tile. The most practical method of reducing heaving is to leave some residue on the surface over winter. This reduces heaving because it insulates the soil and reduces the amount of freezing and thawing. Fields not harvested last fall will usually have less heaving that those with fall growth removed. Planting a grass with the alfalfa has not been shown to reduce heaving of the alfalfa in the stand. Neither is there any indication of genetic variation in alfalfa varieties for difference in heaving.