Update on winter wheat growth and development in Kansas
Relative to the historical sowing pattern for Kansas, about 65% of the wheat crop was sown late. Excessive moisture during late September – early October is the reason for the delayed sowing. In the majority of the cases this moisture led to a very good stand establishment which is extremely important in setting the crop’s yield potential. However, very little precipitation has fallen since sowing across the majority of the state (Figure 1). In fact, a large portion of the wheat growing region in Kansas (central and western Kansas) received less than 0.35 inches of precipitation since November 1, and the southwest corner of the state received zero precipitation. To provide a historical perspective, this results in anywhere from - 0.6 to -3.15 inches departure from normal (Figure 2).
Figure 1. Monthly precipitation summary for Nov. 1 – Nov. 30 across Kansas.
Figure 2. Departure from normal precipitation for Nov. 1 – Nov. 30 across Kansas.
Late sowing and dry fall implications
The late sowing coupled with a lack of significant precipitation in a large portion of the Kansas wheat growing region might bring challenges to the wheat crop, especially in making it through the winter (Figure 3). Dry conditions may reduce the soils ability to buffer temperature changes at the crown level. Additionally, late sowing and dry conditions might impact secondary root development, which would render the crop less winter-hardy.
Figure 3. U.S. Drought monitor indication that most of the southwest/south-central region of Kansas is experiencing some level of drought stress. Source: http://droughtmonitor.unl.edu/
Late-planted wheat following a summer crop, or delayed by October moisture
In most regions of Kansas where wheat sowing was delayed due to early October precipitation, wheat is behind in development compared to the historical average. Many wheat fields in central and north central Kansas were delayed even further as producers finished summer crop harvest after the rainfall events. In these situations, it was not uncommon for producers to sow wheat after the first of November. This may not have provided the crop enough time to tiller during the fall. One example of such case is shown in Figure 4, where the upper panel reflects a crop sown in early October and the lower panel a crop sown in mid-to-late October. Both photos were taken in nearby fields in north central Kansas (west of Belleville). The better development of the early-October sown fields is apparent when compared to the later sown fields. 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).
Figure 4. Upper panels reflect early October sown field (left) and plant (right) and lower panels reflect a wheat field (left) and plant (right) sown in the last ten days of October. Photos by Guilherme Bavia, assistant scientists, K-State Wheat and Forages Production Group.
Figure 5. Differences in wheat growth and development as affected by planting date. Wheat planted late October showing no primary tillers (left), while wheat planted 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, by Romulo Lollato, K-State Research and Extension.
What should producers look for?
Producers can assess the status of their wheat crop going into the winter 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 aren’t 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 in the right photo (early-October planting). 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 cattle were grazing on this wheat, they would probably pull the plant out of the ground as there aren’t 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, by 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.
Figure 7. Fall growth and development of wheat as affected by planting date. 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 (note Figure 8B below), 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. 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 couldn’t pull the plants out of the ground. Photos by Jim Shroyer, professor emeritus, K-State Research and Extension.
Romulo Lollato, Wheat and Forages Specialist
Mary Knapp, Weather Data Library