Posted February 26, 2021
Plant development, environmental factors influence survivability
How cold is too cold for winter wheat? As frigid Arctic air descended into Kansas two weeks ago, that question — along with single-digit temperatures and below-zero windchill — made Kansas farmers shiver. The answer depends on plant development before the freeze and environmental factors during the event.
“This year is a tale of two crops that had the potential to handle the freeze quite differently,” said Romulo Lollato, a wheat production specialist with K-State Research and Extension. “Early planted fields — which often have too much biomass heading into a freeze — actually had developed cold-hardiness and have the best yield potential for this year’s harvest thus far. In contrast, the late-planted crop suffered from a lack of moisture in the fall and did not have sufficient plant development to withstand the extreme cold. Overall, this plant development combined with specific environmental factors is going to dictate the extent of damage from the freeze.”
The wheat crop’s condition going into the freeze is the first indicator of survivability. To fully understand this crop’s condition, one must go back to the planting date.
Fields planted early in 2020 that caught rainfall in mid-September likely had good stand establishment and early root development. Fields that emerged by the first week of October likely produced more tillers and deeper roots.
In contrast, wheat planted relatively on-time in October or late had lower emergence rates and limited early plant development due to the lack of precipitation through November. According to K-State agronomy, total precipitation from Sept. 1, 2020, through Feb. 8, 2021, was less than four inches for a large chunk of Kansas wheat fields.
“We got the wheat up and growing, but do not have enough moisture to set brace roots,” said Gary Millershaski, who farms in Lakin, in a report to U.S. Wheat Associates on Feb. 18 (https://www.uswheat.org/wheatletter/historic-freeze-severe-dryness-challenge-u-s-winter-wheat-crop/). “We had a couple of inches of snow, but temperatures of 19 degrees Fahrenheit below zero tell me half of the tillers might not make it.”
Air temperature and snow are just two of the environmental factors that affect the extent of winterkill damage. Anyone who stepped outside in the Arctic air felt just how cold it got. A well-tillered wheat field is better equipped to handle extreme cold, but a less-developed crop is more sensitive to air temperature and cannot withstand as cold of temperatures.
The more telling temperature measurement, however, is under the soil surface. Soil temperatures in the single digits can cause winterkill, which did happen in various locations around the state.
“While average soil temperatures in the Feb. 10-27 period were usually above 20 degrees Fahrenheit, the lowest soil temperatures dropped as low as 5 to 14 degrees Fahrenheit,” stated a recent K-State Agronomy eUpdate. “Soil temperatures in the low teens or single digits occurred mostly in northwest Kansas but were also present in parts of southwest and central Kansas.”
Not all hope was lost. Soil moisture content and snow cover help buffer low air temperatures. Dry conditions and dry, light-weight snow do dampen this buffering effect. However, while wheat fields in central Kansas received practically no snow, many areas in the growing region received one to two inches, with the furthermost northern and southern borders receiving up to four inches.
One less-chilly weather factor was that the regions that received the most snow had the lowest minimum soil temperature, meaning the most vulnerable wheat theoretically had more protection from the extreme cold.
“Usually, one to two inches of snow is the minimal amount that would provide a good buffer against cold temperatures, but it got so cold that this effect may have not been sufficient,” Lollato said. “While our stations showed soil temperatures above single digits — a good indication — the sensors are two inches below the ground. Because the crown of the plant is higher in the soil profile — one inch — these borderline temperatures do make us a bit concerned.”
No one knows the immediate impact of this cold weather event. The potential for winterkill in the Kansas wheat crop — especially fields that emerged late — is a cold, hard truth. Central Kansas had limited snow cover (less than two inches), while northwest Kansas saw soil temperatures descending into the low teens to single digits. However, other areas — like south-central Kansas — had more soil moisture and snow depth that protected the early emerged crop.
Farmers will need to monitor the crop as spring development starts and wheat fields green up. Winterkill may be immediately apparent, or injured wheat may green up and then regress. When spring development starts, farmers should check for new leaf growth and evaluate the health of the crown. A whitish, sturdy crown indicates a healthy plant, whereas a brown, mushy color indicates the plant may be in trouble.
“There’s no way to tell the extent of the damage, but by mid-March when fields start to green up, we will know what we are facing,” said Justin Gilpin, Kansas Wheat CEO. “The next two months are critical and precipitation could improve recovery potential.”
Learn more about how the potential for winterkill in the Kansas wheat crop at https://eupdate.agronomy.ksu.edu/article_new/potential-for-winterkill-to-the-kansas-wheat-crop-428-1
Written by Julia Debes for Kansas Wheat