Although alfalfa is dormant during winter, its roots and crown are still alive and respiring slowly. Respiration uses oxygen and produces potentially toxic gases like carbon dioxide, ethylene and methanol.
A solid layer of ice prevents the exchange of gases between the soil and the air above it. Oxygen can’t get into the soil to support respiration and the toxic gases can’t escape. As a result, alfalfa plants suffocate and die.
Predicting when and how much damage ice sheets will cause is difficult. Typically, it takes three to four weeks of solid coverage for ice to kill alfalfa; however, any breakage, thawing, or pores in the ice sheet can enable some gas exchange to occur and reduce or eliminate alfalfa injury. Nonetheless, plants still may be weakened by even short-term ice coverage.
Unfortuntely, there is nothing you can do to help your ice-covered alfalfa plants. While some people have tried to break ice using a tractor and disc or other implement, this doesn’t seem to work well. What you really need to do is wait until green-up in spring and then check your alfalfa early to determine potential loss. Then, and only then, can you make a wise decision about maintaining this stand or planting a new one.
Bruce Anderson
Extension Forage Specialist
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