By Jean Caspers-Simmet
simmet@agrinews.com
WATERLOO, Iowa — Farmers are wondering if their alfalfa fields made it through the winter.
"There was extended icy snow cover over the winter," said Brian Lang, Iowa State University Extension field agronomist.
Lang explained that as alfalfa overwinters it continues metabolic activities at a slow rate.
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"The importance of good fall management — allowing alfalfa to store carbohydrate reserves before winter — is to have these carbohydrates to carry out the over-winter metabolic activities," Lang said. "This function also releases waste products such as carbon dioxide, which escape as gases from the proximity of the plant’s root and crown."
During a winter when significant amounts of ice cover the ground, these gases can’t escape, Lang said. Too much waste product around the root and crown is toxic to alfalfa. Alfalfa can usually tolerate about three weeks of significant ice cover before being overcome.
Lang said that January brought significant snow melt that caused ponding and subsequent "ice skating rinks" in low areas of some fields. These "ice ponds" were thick enough and lasted long enough that alfalfa underneath died.
"Fortunately there are not a lot of these areas or they are not very large," Lang said.
Of more concern are larger areas of fields that had one or more wet snows that settled and remained most of the winter.
Lang said that if the snow was porous waste gases escaped. Stubble that poked through the icy snow cover also avoided this problem.
"The question is were some icy-snow areas dense enough, long enough to cause some damage," Lang said.
Lang looked at a few alfalfa fields including several near Waterloo, and he expects to do more extensive scouting this week. Agri News will share what he finds.
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"So far, where there was good fall growth or where harvest left good fall stubble, fields are fine," Lang said.
He still needs to look at fields that were cut short in late fall, and he also needs to evaluate fields in Dubuque, Delaware, Clayton and Allamakee counties.
No fall stubble, higher metabolic rates for less cold-tolerant varieties, lack of disease resistance, stresses from lower soil fertility, more intense harvest schedules, age of stand and field drainage all impact survivability.
He urged farmers to check their fields.
"Some stand reduction is expected every year," Lang said. "Aside from plant-to-plant competition other stresses can take a toll. So even if winter survival is generally good, some stands will still need to be evaluated this spring."
