The potential ice damage to alfalfa plants was addressed by Dr. Dan Undersander, Extension forage agronomist at the University of Wisconsin-Madison in the recent Wisconsin Crop Manager newsletter. While there is concern about ice, there is nothing that can be done now to minimize potential damage to alfalfa stands.

Even though alfalfa is dormant, the plants need oxygen during the winter. The oxygen comes from air above the ground diffusing into the soil. A solid layer of ice restricts air diffusion and suffocates alfalfa, notes Undersander. This is the common reason for loss of alfalfa plants in low spots in fields.

In assessing potential damage, one must consider whether the ice is in a solid sheet. If the ice is disuniform, cracked, or has holes, it will not completely restrict air movement into the soil and may result in little or no damage. In addition, alfalfa stems sticking up through the ice will help create air holes in the ice. This explains the general recommendation to leave six to eight inch stubble when taking a dormant or late season harvest.

What is the condition of alfalfa stands now? Undersander indicates that alfalfa generally had good hardening (acclimation to cold temperatures) last fall. Hardening decreased the water content outside of plant cells, increased bound water within cells, and increased cell solutes, all of which increase the ability of alfalfa to withstand cold temperatures.

In addition, most of the ice is on top of a layer of snow. This snow provides some oxygen to the soil and will allow the ice to break up naturally and develop cracks for air diffusion.

Alfalfa producers know that snow acts like a layer of insulation protecting the plant from cold temperature. Temperatures below 15 degrees F in the crown region (one to four inches into the soil) will result in damage to alfalfa.

Can anything be done now to lessen the ice accumulation? Undersander says, not really. Trying to break the ice with some type of tillage tool is not recommended because of potential physical damage to plants and exposure of some crowns to colder air temperatures.

Application of fertilizer on top of the ice is not recommended either. This idea comes from the fact that salt in the fertilizer will melt through the ice and cause holes to let air into the soil. Fertilizer typically does not melt all the way through the ice and surface applied fertilizer could cause a runoff problem if rapid melting or rainfall would occur.

Having the ice on top of snow is to the alfalfa plant's advantage. All that can be done at this time is to wait to see what happens, concludes Undersander.