Severe cold this winter, especially in areas with little to no snow cover, could result in damaged or killed stands of alfalfa. According to the American Society of Agronomy, following a cold winter in 2013, 93% of alfalfa growers surveyed in Wisconsin and Minnesota reported alfalfa winterkill or injury, with many reporting losses greater than 60%.
Re-planting alfalfa into those winter-killed fields generally results in poor stands and low productivity due to autotoxicity. According to a report from University of Wisconsin Extension, if alfalfa must be planted in the same year an old stand is killed, a late-summer seeding represents the best option. You can expect some yield reduction though. Overall, the best way to avoid autotoxicity is to rotate to some other crop such as corn for at least a year before seeding the same field back to alfalfa. This, according to UW Extension, allows time for degradation and leaching of soil toxins. The degree of toxicity is directly related to the amount of time between killing the old stand and establishing the new stand.
Knowing that annual forages can provide a productive option in killed alfalfa fields, University of Minnesota researchers conducted trials to determine which crops provide the best returns. They found that annual ryegrass provides a good combination of yield and forage quality, while capitalizing on soil nitrogen left behind by the alfalfa.
“Our work suggests that annual ryegrass is the most reliable and economically viable option to providing early season forage with alfalfa winterkill,” says M. Scott Wells, an extension specialist at the University of Minnesota.
While testing a selection of annual forage crops in winter-killed alfalfa, the researchers also experimented with applying nitrogen to the new crop, and found little to no economic benefit. In their tests, soil nitrogen left from the alfalfa generally met the needs of the annual forage crop.
Read more from the American Society of Agronomy.