Rainfall and cold temperatures will potentially delay wheat-sowing progress in Kansas
Precipitation events during October 1 – 12 period brought to the Kansas wheat growing region anywhere from ~0.46 inch precipitation in the far northwest to as much as 9.7 - 12.6 inches in portions of south central and northeast Kansas (Figure 1). This early-October precipitation resulted in fields with a saturated profile for most of the state, but also water logged conditions that stopped fieldwork. In addition to the excessive moisture, air temperatures and soil temperatures decreased during the same period (Figure 2). The change in soil temperatures was also very rapid and some locations experienced a 20 degree F drop in soil temperatures in the last week alone (Figure 3). Decreased soil temperatures during this crucial period can delay wheat emergence and expose seed to a prolonged time of sub-optimal conditions.
Figure 1. Cumulative precipitation during October 1 – 12, 2018. Map by K-State Weather Data Library.
Figure 2. Current (left panel) and weekly average (right panel) soil temperatures at the 2-inch depth for the State of Kansas. Maps by Kansas Mesonet (http://mesonet.ksu.edu/agriculture/soiltemp).
Figure 3. Soil temperatures at Cheyenne at both the 2-inch and 4-inch depth (mesonet.k-state.edu/agriculture/soiltemp/).
These suboptimal conditions to field work caused by the excessive rains will probably result in a delay in sowing progress in Kansas, although this delay has not yet been noted in the current USDA planting progress report as of October 9 (Figure 2). If producers are forced to delay sowing past their optimal window, wheat fall growth might be compromised due to less time to tiller, which might require some management adjustments to maximize crop productivity.
Figure 4. Wheat sowing progress in Kansas during 2018 (dashed line) as compared to the 1994 – 2016 average (solid line) and range (purple area). Wheat area sown in the current year was on pair with the long-term average as of the latest USDA report (Oct. 9), but this is likely to change in the next report due to the excessive rainfall conditions around the state. Graph based on USDA-NASS crop report of progress as of October 9, 2018.
Management adjustments to consider when sowing is delayed past optimum sowing window include:
- Increase seeding rate: Planting late will decrease the crop’s fall tillering potential. Tillering is related to temperature and moisture availability, with higher temperatures resulting in more tillers. As planting is delayed, the crop will have less time to tiller in the fall, thus relying more on the primary tillers. Therefore, we recommend increasing plant population to compensate for the reduced tillering capacity. For every week planting is delayed beyond the end of the optimal planting date range, there should be corresponding increase in seeding rates of between 150,000 – 225,000 seeds per acre (or 10 to 15 lb/acre) in western Kansas, or 225,000 – 300,000 seeds per acre (15 – 20 lb/acre) in eastern Kansas. There is a point of diminishing return, of course, and final seeding rate should not be above 90 pounds per acre in western Kansas and 120 pounds in eastern and central Kansas for grain-only wheat production.
- Place starter phosphorus (P) fertilizer with the seed: Phosphate-based starter fertilizer promotes early-season wheat growth and tillering, which can help plants compensate for the delayed sowing date. Additionally, P is less available under colder soil temperatures, which can result in P deficiency under cold weather conditions. When planting late, producers should strongly consider using about 20-30 lbs/acre of P fertilizer directly with the seed, regardless of soil P levels. This placement method is more effective late in the year because the fertilizer is placed to the seed, allowing rapid access to these critical nutrients.
- Use fungicide seed treatment or plant certified seed: Late-planted wheat is sown into colder soils, which generally increases the time needed for germination and emergence to occur. As a consequence, there is increased potential for seed decay and soil borne diseases on seedlings plants. Fungicide seed treatment can reduce the risk of disease for about 3-4 weeks and improve the chances of getting a good stand established. It is important that the seed treatment thoroughly coat the seeds to ensure good protection. For fungicide seed treatment options, please refer K-State’s fungicide seed treatment chart available at: https://www.bookstore.ksre.ksu.edu/pubs/MF2955.pdf
- Wheat variety differences: Wheat varieties with good tillering ability may offset some of the consequences of late planting, as it might still be able to produce one or two tillers during the fall whereas a low- tillering variety may produce no fall tillers. Also, late- planted wheat is typically behind in development going into the winter, which might translate into slower development in the spring. This delay can increase the risk that the crop will be exposed to moisture stress and heat stress during grain filling period that is critical for grain yields. Therefore, selecting an early-maturity variety with good yield potential may help offset the negative consequences of late planting
On a final note, a couple of positive things about the sowing progress delay are that: (i) the majority of the state have a good profile moisture, which will not only ensure good stand establishment but also possibly contribute to wheat grain yield potential; and (ii) late-planted fields are less likely to be infected with wheat streak mosaic, as the wheat curl mite populations would be more active in warmer temperatures generally observed under early planting. Thus, we are probably decreasing the risk of another wheat streak mosaic outbreak due to the delayed planting.
Romulo Lollato, Extension wheat and forage specialist
Erick DeWolf, Extension wheat pathologist
Mary Knapp, Weather Data Library
Christopher Redmond, Kansas Mesonet