This could be a tough winter for alfalfa in Kansas, especially newly seeded stands on fields where there was no snow cover, says Jim Shroyer, Kansas State University Extension crop production specialist.
“If the plants are damaged by winterkill, the taproot will turn soft and mushy,” says Shroyer. “Producers should check for bud and new shoot vigor. Look for delayed green-up, lopsided crowns and uneven shoot growth. If you see any of these symptoms, check the taproots for firmness. Some plants may even begin to green up and then die. But plants that put out second leaves are probably fine.”
If some plants are injured and stands have been thinned, producers may wonder about thickening the stands. Shroyer advises caution.
“Interseeding alfalfa to thicken an alfalfa stand will generally not work. If the stand is one year or less old, new seedlings will generally come up and then be outcompeted by the survivors from last year. If large areas of a one-year-old field have been killed, those areas can be disked and then seeded. If the stand is two or more years old, interseeding alfalfa will not work because of allelopathic effects from the established plants.”
This winter could also result in a more common form of injury to alfalfa. As the soil freezes and thaws, alfalfa stands can be damaged by the heaving effect.
“This winter has been cold enough to freeze the soil where it is not under snow cover. Soils with high levels of clay are especially prone to winter heaving,” Shroyer says.
If heaving has occurred, dig up some plants to determine if the taproot is broken.
“Plants with broken taproots may green up, but they perform poorly and eventually die. Slightly heaved plants can survive, but their longevity and productivity will be reduced. Crowns that heaved one inch or less are not as likely to have a broken taproot. With time, these plants can reposition themselves. Raised crowns are susceptible to weather and mechanical damage. Raise cutterbars to avoid damaging exposed crowns.”
Producers can start to evaluate the health of their alfalfa stands as soon as the soils thaws, Shroyer says. “They should look at the crowns and roots. Buds should be firm, and white or pink in color if they have survived with good vigor. The bark of roots should not peel away easily when scratched with a thumbnail. When cut, the interior of healthy roots will be white or cream in color.”
When alfalfa growth reaches 4-6” producers can use stems per square foot to assess density. A density of 55 stems per square foot has good yield potential. There will probably be some yield loss with stem counts between 40 and 50 per square foot. Consider replacing the stand if there are less than 40 stems per square foot and the crown and root health is poor, he says.