Update on winter wheat growth and development in Kansas
While most of the 2019-20 Kansas wheat crop was sown relatively on time compared to the historical sowing pattern for Kansas (with the exception of some fields planted after a late-harvested soybean crop), the fraction of crop emerged is below average (Figure 1) and some of the emerged fields are in rough shape. Reasons for the delayed emergence include below-average precipitation and temperatures during the fall, which occurred in a large portion of the wheat-growing region in Kansas (central and western Kansas). For instance, central Kansas has received just 2 to 4 inches of precipitation since September 1. To provide a historical perspective, this results in anywhere from 3.0 to 4.5 inches below normal (Figure 2). In western Kansas, southwest in particular, the situation is even worse. The region received on average 0.3 to 2.5 inches of precipitation, which does not allow for optimum emergence of fall-planted crops (Figure 2).
Figure 1. Kansas winter wheat progress as depicted by USDA-NASS. Upper panel shows percent of crop in good-excellent conditions; middle panel shows crop condition distribution across all levels; and lower panel shows crop planting and emergence progress. (Figure adapted from: https://www.nass.usda.gov/Charts_and_Maps/Crop_Progress_&_Condition/2020/KS_2020.pdf).
Figure 2. Planting season precipitation (left) and departure from normal (right) for Sep. 1 – Nov. 30 across Kansas. Source: Weather Data Library.
Implications of a cool and dry fall
Below-average precipitation in a large portion of the Kansas wheat growing region reduced soil moisture availability (Figure 3). This might bring challenges to the wheat crop, especially for stand establishment and tillering, which would render the crop less winter-hardy and could result in winter survival issues (Figure 3).
Figure 3. Percent soil saturation as of December 3, 2019. Source: Kansas Mesonet
In most of Kansas’ wheat growing region, wheat development is lagging compared to the historical average. Dry soil conditions precluded emergence in many fields, and those fields that emerged are not, on average, well developed due to a combination of dry and cool conditions. This combination may not have provided the crop enough time to tiller during the fall. One example is shown in Figure 4, where there is a comparison of fields planted in late September, late October, and early November. While these photos were taken in 2018, a very similar situation is true this year – although for a very different reason. In 2018, stand establishment was delayed due to excessive fall moisture precluding field activities (planting), while in 2019 planting typically occurred on time but dry soils and cool temperatures delayed stand establishment.
Figure 4. Late September (left) versus late October (center) versus early November (right) sowing dates and their effect on canopy development. Photos taken December 10, 2018 in Hutchinson by Leonardo Molssato, Assistant Scientist, K-State Wheat and Forages Production Group.
Figure 5. Differences in wheat growth and development as affected by planting date. Wheat planted in late October showing no primary tillers (left), while wheat planted in early October has started to tiller (right). Both crops still need significant fall growth to properly prepare for winter dormancy. Photo taken at the Agronomy North Farm, Manhattan, Romulo Lollato, K-State Research and Extension.
What should producers look for?
Producers can assess the status of their wheat crop in a few different ways. One important way is looking at the top-growth and counting leaves and tillers. As mentioned previously, wheat needs at least 4-5 leaves and 1-2 tillers prior to winter dormancy for maximum cold tolerance. Wheat that has fewer tillers and leaves will be more susceptible to winter kill (Figure 5).
It is important to also look at the root system development (Figure 5). Roots coming out from the seed are called seminal roots and are used to take up water and nutrients throughout the entire growing season. There are not very many of these roots, so their contribution to overall water and nutrient uptake is limited. Crown roots are illustrated in Figure 6, right panel. Crown roots are the two white protrusions coming out of the white area about an inch above the seed. These roots take up most of the water and nutrients needed by the plant, and they are very important for the plant to survive the winter. If a cow were grazing on this wheat, she would probably pull the plant out of the ground as there are not many roots holding the plant in the soil yet. Consequently, this wheat crop still needs considerable fall growth prior to grazing or winter dormancy.
Figure 6. Seminal and crown roots development in wheat as affected by planting date. Both rooting systems are developed enough to be grazed, and may be susceptible to nutrient deficiencies or desiccation damage over the winter if the crown roots develop further. Photos taken at the Agronomy North Farm, Manhattan, Romulo Lollato, K-State Research and Extension.
The photos below illustrate various degrees of what you would like to see when you examine your wheat this fall. As expected, there is better canopy coverage with early-planted wheat for dual purpose (mid-September planting) as compared to wheat planted at the optimal planting time for grain only (mid-October planting). This does not necessarily mean the early-planted wheat is in better condition for winter. As long as the wheat planted in mid-October has 1-2 tillers and good crown root development (Figure 8B), the plants will have adequate growth going into winter. In addition to having adequate top-growth and root development, factors such as the extent of the plants’ cold hardening, variety differences in winter hardiness, soil moisture and temperature, and snow or plant residue protection on the soil surface will ultimately have an impact on winter survival.
Figure 7. Fall growth and development of wheat as affected by planting date. Photos by Romulo Lollato, K-State Research and Extension.
Figure 8. (A) Some of the crown roots are over one-inch long. For this plant, a couple additional weeks of mild weather would allow for more root growth which would be desirable. (B) Ideal wheat above- and below-ground development before winter dormancy, with crown roots fully developed and able to provide water and nutrients to the plant. With this amount of crown root development, wheat plants should be well anchored. If cattle were grazing this wheat, they could not pull the plants out of the ground. Photos by Jim Shroyer, professor emeritus, K-State Research and Extension.
Stay tuned to future issues of the eUpdate for more information on the status of the 2020 wheat crop.
Romulo Lollato, Wheat and Forages Specialist
Mary Knapp, Assistant State Climatologist and Weather Data Library