By Marvin Hall
Now is the time to scout for alfalfa frost heaving so that preparations can be made if the stand will need to be rotated out this spring. Here are some answers to frequently asked questions about frost heaving of alfalfa.
Is there anything that can be done to push the crown back into the soil?
No. While many people have tried cultipackers or lawn rollers to push the heaved alfalfa crown and root back into the soil, there is no data suggesting that any of these techniques are beneficial.
How much frost heaving is needed to justify rotating an alfalfa field into another crop?
The answer to this question depends on the severity of the heaving. Consequently a complete evaluation of the stand is needed. Depending on when the crowns were elevated above the soil, all of the crown buds could have been frozen and the plant is essentially dead. Look for green growth coming from the crown and count the number of these crowns per square foot. If there is an average of five or more live crowns per square foot then the stand is probably worth keeping at least through the first harvest.
Will the alfalfa that is still alive remain productive throughout the season?
Frequently, alfalfa plants that have heaved only a small amount (one inch or less) still have their tap root intact and can remain productive. Caution must be used to insure that the crown is not removed when cutting the alfalfa during harvest. These crowns will also receive additional damage from wheel traffic with each harvest which kills additional crown buds and exposes the crown to more diseases.
Fields in which alfalfa crowns have heaved a lot (greater than 1 inch) are strong candidates for rotation into another crop. However, if there are greater than five live plants per square foot then it may be best to take an early first harvest prior to rotating. Plants with their crowns elevated to this height generally have their tap root broken and will be more susceptible to drought stress (low production) this summer. In addition, crowns at this height can be cut off during the first harvest leaving the root with no growing points for herbage regrowth.
How can I tell if the alfalfa is worth keeping after the first harvest?
As mentioned earlier, the number of crowns per square foot is one method for determining alfalfa stand productivity. Another determinant is the number of stems per square foot. As the stem number declines to 40 stems or less per square foot alfalfa fields begin to loose profitability and should be rotated out of alfalfa.
Will the heaved alfalfa survive another winter?
Unfortunately, the crown buds (from which spring growth comes from) of heaved alfalfa plants will be exposed to colder temperatures next winter because the crowns will not be insulated by the soil. Exposure to freezing temperatures next winter may kill the crown buds. If an alfalfa field with heaving this spring is kept until next spring it should be monitored very closely with anticipation that it should be planted to another crop.
Source:psu.edu