Authors: Romulo Lollato, Mary Knapp

The 2017-18 Kansas wheat crop has been exposed to a wide range of extreme weather conditions since its sowing in the fall of 2017. It started with an extremely moist October where as much as 7 inches of precipitation fell and delayed wheat sowing across the majority of the state, resulting in the slowest sowing pace since 1994 (see more details in the article “Kansas wheat crop progress as of mid-November 2017”, eUpdate Issue 662, November 17, 2017). The delayed sowing resulted in a less-developed crop going into the winter which becomes more susceptible to potential winterkill due to less fall tillering and less time to acclimate to cold conditions. Consequently, two very cold events during January caused concern for wheat producers in north central and southwest Kansas (see more details in the article “Possible impacts of the recent cold weather to the Kansas wheat crop”, eUpdate Issue 667, January 5, 2018; and “Update on possible impacts of January's cold temperatures to the Kansas wheat crop”, eUpdate issue 669, January 19, 2018). Since then, the most widespread concern has been the lack of topsoil moisture, coupled with an underdeveloped rooting system due to a combination of late sowing and dry fall conditions. In this article, we aim to update the current conditions of the Kansas wheat crop in face of all the adversities described above.

Precipitation totals during the growing season

Total precipitation from October 1, 2017 until March 13, 2018, or roughly the winter wheat growing season, ranges from less than one inch in southwest Kansas to more than 12 inches in southeast Kansas (Figure 1). These totals correspond to a departure of -1.5 inches in northwest Kansas to as much as -5 inches in south central Kansas (Figure 1) as compared to the 1981-2010 normal.

However, the bulk of this precipitation occurred during the month of October and the majority of Kansas has had little to no precipitation since then. As a consequence, total precipitation during November 1, 2017, to March 13, 2018, ranges from zero inches, particularly counties in southwest Kansas, to about 6 inches in southeast Kansas (Figure 2). The majority of the wheat growing region received anywhere from zero to no more than 1.66 cumulative inches, which corresponds to departures from the normal ranging between -6.7 to -0.72 inches (Figure 2).

The U.S. Drought Monitor indicates that a greater proportion of the state is under drought conditions as compared to 2012, a year where drought was accentuated and reduced wheat yields across Kansas (Figure 3). Figure 3 also shows a comparison of drought conditions experienced during mid-March 2013 and 2014. Unless spring weather conditions result in above-average precipitation and below-average temperatures, the current drought will likely impact wheat yields from a statewide perspective. For instance, for the years highlighted in Figure 3, USDA-reported state level wheat yields were 42 bu/ac (2012), 38 bu/ac (2013), and 28 bu/ac (2014).

Figure 1. Cumulative (left panel) and departure from the normal (right panel) precipitation from October 1, 2017, to March 13, 2018. Source: Weather Data Library.
Figure 2. Cumulative (left panel) and departure from the normal (right panel) precipitation from November 1, 2017, to March 13, 2018. Source: Weather Data Library.
Figure 3. Drought conditions as of March 13, 2012 (upper left panel), March 12, 2013 (upper right panel), March 18, 2014 (lower left panel), and March 13, 2018 (lower right panel). The U.S. Drought Monitor suggests a larger proportion of the state is under extreme, severe, moderate, and abnormally dry conditions. Source: http://droughtmonitor.unl.edu/

Air temperatures

Mean air temperatures during the 2017-18 winter wheat growing season were below the long-term normal for the majority of Kansas both during the fall and the winter (Figure 4). Temperatures have been as much as 9.7 degrees F below-normal during the fall, and 11.3 degrees F below-normal during the winter. Cooler temperatures during the fall decreased canopy and root development. The crop could potentially have benefited from slightly warmer temperatures to enhance tillering, fall canopy closure, and crown root elongation. However, cooler temperatures during the winter have likely been beneficial, especially recently, for slowing the crop development down. In fact, by this time in both the 2015-16 and 2016-17 growing seasons, the majority of the varieties had already reached the first hollow stem stage of development in Hutchinson, while none have reached it yet this season (please see accompanying eUpdate article, “Wheat first hollow stem update: March 14”. The reason why cooler-than-average temperatures have likely benefited the crop is that once temperatures increase in the spring, the crop takes on spring growth and increases in biomass, consequently increasing its water demand. Thus, increased water demand in dry soils would result in abortion of older leaves and potentially of older tillers.

Figure 4. Departure from the normal seasonal mean temperature for the fall (left panel) and winter (right panel) periods during the 2017-18 winter wheat growing season. Source: Weather Data Library.

Crop condition

The majority of the Kansas wheat crop has started to greenup with the increasing day length and temperatures in late February – early March (Figure 5). It is clear from Figure 5 that vegetative conditions this growing season are not as poor as those experienced in the 2012 drought for western Kansas, but that the crop is in the worst condition in the south central portion of the state.

In portions of Kansas where some level of precipitation was received from snowfall or freezing rain events in January and February, the crop is thus far standing in, expecting a rainfall. However, due to high rainfall totals in October followed by extremely dry conditions, the topsoil across the majority of Kansas is extremely dry, however there might still be some subsoil moisture (Figure 6). In many cases, however, due to the cooler-than-average temperatures, the crown roots have not developed enough to reach the subsoil moisture and are several inches away from it.

Figure 5. Comparison between vegetation conditions (represented as Normalized Difference Vegetative Index, NDVI) on March 13, 2012 and March 13, 2018.
Figure 6. Mismatch between crown root placement (restricted development due to low temperatures and dry topsoil) and subsoil moisture remaining from October precipitation. Photo taken near Wellington, Sumner County, south-central Kansas, late February 2018 by Romulo Lollato, K-State Research and Extension.

The situation depicted in Figure 6 is true for many wheat fields across the state. Another more extreme example from western Kansas is shown in Figure 7, where the crown roots are even less developed and there is a mismatch between the seminal roots and the subsoil moisture.

While the wheat crop in central Kansas is, for the most part, hanging in and waiting for additional moisture, portions of southwest Kansas affected by extremely dry conditions already show the older leaves of the crop drying out (Figure 8) and soon, the older tillers may be aborted if no precipitation is received. It is not uncommon to see fields with little to no green due to drought conditions, or portions of the field that show extreme symptoms of drought stress (Figure 8). The southwest portion of Kansas is the region in which the wheat crop is in the most critical condition and desperately needs rain, especially as the temperatures warm up and crop water demand increases in the spring.

Figure 7. Crown roots undeveloped and a mismatch between seminal roots and subsoil moisture remaining from October precipitation. Photo taken in Wichita County, west-central Kansas, mid-March 2018 by Romulo Lollato, K-State Research and Extension.
Figure 8. Drought stressed wheat in western Kansas. The wheat plants depicted on the left are aborting older leaves due to drought stress, and will soon start to abort older tillers if no precipitation is received. The wheat field depicted on the right shows a typical scenario in southwest Kansas, where little to no crop development is observed and the crop is barely visible. Photo on the left taken by Vance Ehmke in Lane County, KS; photo on the right taken by Romulo Lollato in Wichita County, KS.

Romulo Lollato, Extension Wheat Specialist

Mary Knapp, Weather Data Library