Sharp decline in temperatures: Possible impacts on the Kansas wheat crop
The sudden, sharp drop in temperatures across Kansas observed on October 27 could have different consequences, varying from no impact to some injury in particular fields. Temperatures dropped from around 80 degrees F on the afternoon of October 25 to approximately 20 degrees F the morning of October 27, particularly in the western portion of the state (Figure 1).
Figure 1. Hourly temperature dynamics from October 25 through October 27 for Garden City (upper panel), Cheyenne (middle panel), and Manhattan (lower panel). Data courtesy of Kansas Mesonet.
The actual consequences of this temperature drop should be field specific, dependent on the region within the state, and on several other factors. The moisture level in the topsoil will be important to help buffer possible injuries resulting from cold temperatures. Soil moisture is generally good in most of the state due to early-October rainfall, which will cause the soil to have a better thermal buffer capacity, compared to a dry soil. In fact, soil temperatures at the 2-inch depth did not fall below 44 degrees F at any of the K-State Mesonet (http://mesonet.k-state.edu/) weather stations as of October 27 at 7:00 am (Figure 2). These warm soil temperatures could definitely help buffer any negative effects of the sharp temperature drop.
Figure 2. Coldest 2-inch soil temperature as of 27 October 2017, 07:00 am. Minimum soil temperature did not reach values lower than 44°F across the state. Data courtesy of Kansas Mesonet.
Possible exceptions could include fields planted in heavy no-till residue where the furrow might not have been closed properly at sowing, or where there was not good seed-soil contact. Under these circumstances, the lack of furrow closure results in a less protected seedling (and in some fields, crown) which might be more exposed to cold temperatures (Figure 3). Producers are encouraged to start checking for possible injury on lower portions of the fields and especially in no-till fields with heavy residue. The cold temperatures also will be more likely to cause injury to wheat if the plants were showing drought stress symptoms and soil temperature might have fallen below those shown on Figure 2, as dry soils will get colder more easily than wet soils. Additionally, the drier and looser the seed bed soil is, the greater the potential for the planting to be exposed to cold temperatures resulting in injury. Meanwhile, firmer and moister soils should help to minimize rapid fluctuations in soil temperatures allowing the wheat to better withstand cold temperatures.
Figure 3. Effect of soybean residue on wheat cold damage. Yellow portions of the field correspond to greater residue left by the combine at soybean harvest, and resulted in poorer seed-soil contact at wheat planting. As a consequence, the plants are more exposed to colder temperatures and potential injury. Photo provided by Romulo Lollato, K-State Research and Extension.
Another factor affecting wheat’s response to the cold is whether the wheat had time to become properly cold-hardened. It is important to remember that a large portion of the Kansas wheat crop has been planted recently, after the rainfall events of early- to mid-October; therefore, it is still too early to suggest that the wheat has been cold-hardened. In fact, many fields have not even emerged at this point or are just now starting to emerge.
In fields that have not yet emerged but in which seeds are already sprouted, no significant injury should be expected for two main reasons:
- First, recently sprouted wheat generally handles temperatures above 5-10 degrees F well, and air temperatures never reached those levels (Figure 4).
- Secondly, recently sprouted wheat is still below the soil surface and the warm soil temperatures will likely help buffer the seedling from being damaged by the cold.
In fields where the crop has already emerged, temperatures of around 15 degrees F or less can injure the newly emerged wheat, and these limits decrease as the crop progresses to tillering later in the fall and become more cold-hardy. Thus, some fields in western Kansas where the crop has recently emerged, especially the northwest part of the state, could sustain some level of damage. We likely won’t know for sure until temperatures warm up and give us an opportunity to scout.
If fields were affected, the first symptom will be burndown of the wheat from these cold temperatures as shown in Figure 3. If the wheat was bigger-than-normal, the plants may look “rough” with a lot of brown, dead-looking foliage on the soil surface. That doesn’t mean the plants are dead. The important factor will be whether the crown below the soil surface remains alive. Having a well-developed secondary root system will help the plants survive. As temperatures did not drop as low in the central portion of the state, the concern with possible cold injury is not as great as fields that recently emerged in northwest Kansas.
Figure 4. Minimum temperatures observed during the 24-hour period preceding October 27, 2017 at 12:50 PM. Data courtesy of Kansas Mesonet.
The extent of the unusually large and rapid drop in temperatures from well above-normal to well below-normal is a concern in certain scenarios described above. In fields that were planted earlier, if the wheat did not develop sufficient cold-hardiness, it will be more susceptible to injury from the recent cold snap.
Romulo Lollato, Extension Wheat Specialist
Mary Knapp, Weather Data Library
Christopher “Chip” Redmond, Kansas Mesonet Manager