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Late season alfalfa management

Karen Johnson

In the Upper Midwest, many producers have been able to dodge the rain drops to successfully harvest three, if not four, cuts on their alfalfa fields this year. Which begs the question, if the stand is matured enough should we be considering another cutting of alfalfa? If so, what kind of implications will that have on next year’s crop?

There are several factors that contribute to alfalfa stand survival through the winter. The nature of the plant, how it is managed and weather combine to determine the overall stand survival rate.

Nature of the alfalfa plant

As the days get shorter and night time temperatures drop below 40°F, the alfalfa plant begins a process called hardening to prepare for the cold temperatures. During this time, alfalfa begins to accumulate carbohydrates for food reserves. Additional compounds accumulate in the cell to absorb free water protecting the water in a state that will not freeze. The alfalfa plant will lose the remaining water, water outside the cell wall, to prevent the water from freezing and causing damage. This leaves the cells extremely dehydrated over the winter season.

Other factors that can also affect the alfalfa plants ability to survive through winter are:

Managing the plant

The ability of the plant to successfully overwinter starts with proper management. Timing of harvest events, especially in the fall, can either maintain or deplete root reserves critical for winter survival. University experts indicate that there is a critical fall harvest period in which the alfalfa should not be harvested. This period, in Minnesota, usually lands between September 1 and October 15th and is associated with a great risk of reduced yield and stand persistence.

Regardless of the dates, it is critical that final harvest occurs 4 to 6 weeks before the average date of the first killing frost. Cutting during this period interferes with accumulation of food reserves. Additionally, the alfalfa plant will utilize reserves to regrow sacrificing reserves meant for winter. In general, it is recommended to maintain a minimum of 6 inches for stand growth or stubble to aid in snow accumulation for insulation.

Weather

Over the last couple of months, we have been hearing predictions of strong La Nina conditions across the United States. Here in the Midwest, there are predictions of a freezing cold winter with average snowfall ahead of us. According to the Farmers’ Almanac, we could see some snow and cold conditions as early as mid-November, with a mixed bag of winter weather in December and January, and frigid temperatures in February.

In terms of the alfalfa plant, temperatures of 15 to 5°F can cause damage at the crown of the plant. Luckily, snow can serve as an excellent insulator. A minimum of 4 inches of snow is considered adequate to insulate the soil and prevent direct freezing damage to alfalfa. The way in which the freeze and thaw cycles occur and when the alfalfa breaks from dormancy can also have a direct effect on winter survival.

Conclusion

Much like anything in farming, the weather determines the overall outcome of your particular alfalfa survival scenario. We must keep in mind that we may not be able to control the weather or the current variety of alfalfa in the field, but we can control how we manage it. It is important to allow your alfalfa field 4 to 6 weeks before the first killing frost to accumulate the necessary reserves to survive winter. Six inches of regrowth is also essential to promote the necessary snow insulation for minimal winter injury.

References

Cosgrove, Dennis, and Dan Undersander. Focus on Forage. Issue brief. Wisconsin Forage Team, 2003. Web. 14 Sept. 2016.

"2016-17 Winter Weather Forecast - Farmers' Almanac." Farmers' Almanac. N.p., n.d. Web. 14 Sept. 2016.

Noland, Reagan, Doug Holen, Craig Sheaffer, and M. Scott Wells. "Alfalfa Assessment: Factors Leading to Winter Injury." : Forage Production: University of Minnesota Extension. N.p., 2015. Web. 14 Sept. 2016.

September 2016

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