Effect of the recent winter storm on the Kansas wheat and alfalfa crops
The week of January 10 – 16 brought to the Kansas wheat crop some much needed moisture, which was accompanied by a considerable amount of ice -- especially in the southwest portion of the state. Precipitation totals ranged from about 0.25 inch in far northwest Kansas, to just over 3 inches throughout the southern two tiers of counties (Fig. 1). The majority of the state received more than 0.5 inches of precipitation.
Figure 1. Cumulative precipitation for the period encompassing Jan. 10 – 16, 2017.
In addition to this precipitation, the western fifth of the state also got as much as 2.3 inches of snow (Fig. 2). This protects the crop from extreme cold temperatures, although it may not bring much moisture to the wheat crop. Usually, one foot of snowfall brings about 1 inch of moisture; thus, 2 inches might bring approximately 0.15” moisture if the snow persists in the field.
Figure 2. Cumulative snowfall for the period between Jan. 10 – 16, 2017.
These storms were accompanied by relatively mild temperatures throughout the state. In fact, the southern half of Kansas had mean temperatures above 32 degrees F for the Jan. 10 - 16 period, which is about 2 to 7 degrees F or more higher than the historical mean temperatures for the period (Fig. 3). The exception to this rule was in the north, and specifically the northwest section of the state, where temperatures ranged from 27.8 to 30.3 degrees F and were below average by about 2 degrees F.
Figure 3. Mean temperature observed between January 10 – 16, 2017 (upper panel) and the departure from the long-term mean for the same period (lower panel).
Ice storms occur when freezing rain falls for a long period of time, accumulating on roads, trees, and over the winter wheat crop. Most of the ice formation from the recent winter storm seems to have taken place in the southwest portion of Kansas. Central and eastern Kansas received precipitation mostly as rainfall.
Possible consequences to the wheat and alfalfa crops
With exception of the north central portion of Kansas, the majority of the wheat growing region of the state was under some level of drought conditions as of January 10, ranging from abnormally dry in the central and south central portions of the state to severe drought in the far southwest counties (Fig. 4).
Figure 4. Drought indices for the state of Kansas for January 10, retrieved from droughtmonitor.unl.edu.
The possible consequences of the recent winter storm to the wheat and alfalfa crops will depend on drought and crop conditions experienced prior to the storm, total precipitation received, and whether this precipitation resulted in ice formation. Significant improvement in soil moisture occurred in the eastern parts of the state, but only moderate improvements occurred in the west, where precipitation was generally lighter and the drought more severe (Fig. 5).
Figure 5. Drought indices for the state of Kansas for January 16, retrieved from droughtmonitor.unl.edu.
For most of central and southern Kansas, the storm brought some much-needed moisture to both alfalfa and wheat crops. The combination of little to no ice formation and as much as three inches of precipitation means this storm should overall be a benefit to wheat in the state, and more than meet the water needs of winter wheat through the winter. In fact, winter wheat consumes very little water during the winter, with average consumption of less than 0.1 inch per week (Fig. 6). Thus, the range in precipitation received in most of Kansas, which varied from 0.5 to 3 inches, should be very beneficial for the crop, most of which was under some degree of drought stress. Wheat in regions of the state that received about 3 inches or more of precipitation should even have enough soil water now to meet the needs of wheat for a portion of the spring, perhaps up to stem elongation, when winter wheat water needs increase.
Figure 6. Winter wheat weekly water use. Source: Univ. of Nebraska EC731.
In far southwest Kansas, a few different scenarios may take place. In this portion of the state, many wheat fields have not yet emerged or have very scattered emergence at this point, due to the drought conditions experienced throughout the fall. Under these circumstances, precipitation -- either as rainfall or ice -- could possibly benefit the crop, and be sufficient for enabling the crop to emerge.
Previous studies have shown that for a wheat crop sown about one inch deep or less, approximately 0.4 inch of precipitation should suffice for even emergence and a good stand to be established. Thus, the precipitation received in southwest Kansas should be enough to help wheat that has not yet emerged to make it out of the ground as a spring-emerged crop, provided the seed is still viable. Ungerminated seed might not be viable where it started to germinate and then stopped for lack of moisture, or where there has been insect or disease damage, or wildlife feeding. It is important to keep in mind that spring-emerged winter wheat has considerably less yield potential than a fall-emerged crop, and producers will have to decide whether maintaining the crop is a viable option.
Possible ice damage to the wheat and alfalfa crops?
Most likely, there will not be any damage to the wheat or alfalfa crops from ice. For an established wheat crop or alfalfa stand to suffer damage from ice, previous research has shown that a minimum 10 to 40 days of ice surrounding the leaves is necessary. Ice generally damages plants by sealing leaves, stems, and buds, from the surrounding air, creating an anaerobic environment. When ice surrounds the crown of wheat or alfalfa for long periods of time, it allows toxic metabolites resulting from this anaerobic environment (ethanol and carbon dioxide) to build up, preventing the natural gas exchange that occurs during respiration. In other words, it “suffocates” the plants. Still, for suffocation to occur, a long period of ice-covered leaf surface is needed; thus, the crops around Kansas should not suffer from ice damage from last week’s storm.
What to look for
We should not expect widespread cold damage from the recent winter storm, but a few extreme drops in temperature with very little snow cover happened during that fall, which might result in some localized cold damage. It will not be possible to fully know whether winter cold has caused damage to the wheat or alfalfa crops approximately until spring greenup, when the crops are breaking winter dormancy. At that point, it is extremely important to go out and check the fields, preferably sampling some whole plants, before investing any more money in the crop.
For wheat, producers should pull plants out of the ground, pull the leaves back to expose the crown and stems, and check for color. Brown color with shriveled, mushy stems indicate damage and possibly winterkill (Fig. 6). If wheat plants have white stems and a healthy-looking crown area, even a slight amount of injury should not be of major concern. Producers should check to determine plant survival, and set a target of anywhere from 20 to 30 healthy plants per square foot, depending on location within the state (20 plants for the western portion of the state, 30 plants for central and eastern portions). If the final healthy wheat stand is less than 20 to 30 plants per square foot (with approximately 50% of the target stand being a threshold for maintaining or terminating the crop), producers can try to compensate with additional N to enhance spring tillering. If stands are less than about 10 plants per square foot in western Kansas, and 15 plants per square foot in central and eastern Kansas, producers could consider terminating the crop and planting a spring crop as an alternative.
Figure 6. Comparison between a winter wheat plant that suffered winter injury, characterized by brown crown and shriveled stems (left panel) and a plant that shows only minor symptoms of cold damage (brown leaves) but overall has white and healthy stems (right panel). Photos by Sandra Wick, K-State Research and Extension.
For alfalfa, the procedure should be similar. Producers should use a spade to cut into the taproot and crown, and check whether the color is a healthy whitish-beige, or a darker brown, which would be an indicative of a cold-damaged crown. Additionally, producers should look for newly appeared green crown buds at ground level. A good goal to shoot for is approximately 30 vigorous stems per square foot. If poorer stands are found, producers can consider a soil test to determine whether added nutrients are needed. Another option is to delay the first harvest to beyond the late bud stage, which would decrease the quality of the first cut but result in more reserves for regrowth, most likely improving persistence of the stand.
Romulo Lollato, Wheat and Forages Specialist
Mary Knapp, Weather Data Library