Ensuring that the wheat crop is sown during the optimum window of sowing dates and seeding rate are two steps needed to help ensure that the crop can reach its maximum yield potential (Figure 1). Sowing date affects yield potential due to its effect on stand establishment, soil and air temperatures to which the crop is exposed, tiller formation, disease pressure, and more. The optimum seeding rate will vary based on sowing date, and its adjustment is crucial to ensure the crop can maximize its yield potential.
Figure 1. Best management practices to be adopted before and after planting to ensure maximum yield potential can be attained in a given growing season. Schematic representation by Romulo Lollato, K-State Research and Extension.
- Sowing dates
a) K-State recommendations
Optimum sowing date for winter wheat is quickly approaching for a large portion of Kansas (Figure 2). Depending on geographical location, optimum sowing window can start as early as September 10th and last until the end of September (northwest Kansas), or it can start as late as October 5th and last until October 20th (southeast Kansas). This gradient in sowing dates, with earlier dates in the northwest, is a function of temperature. Northern regions will have cooler air and soil temperatures earlier in the year as compared to southern regions.
Figure 2. Optimum planting dates for winter wheat according to geographical location within Kansas. Figure adapted from K-State Research and Extension publication L-818, Kansas Crop Planting Guide.
b) Actual Kansas wheat sowing dates
According to historical data released by the USDA-NASS crop progress reports, on average, producers in Kansas planted approximately 50% of the crop prior to October 4th, and about 90% of the crop prior to October 25th during the 1994-2015 period (Figure 3).
Figure 3. Average percent wheat area planted in Kansas after September 1st. Data represents average and standard deviation for percent planted area during the 1994-2015 period as reported by the USDA-NASS Crop Progress Reports (https://www.nass.usda.gov/Publications/National_Crop_Progress/).
Although 50% of the fields are, on average, planted by Oct. 4th, there is a large year-to-year variability (see error bars on Figure 3). This year-to-year variability is driven by sowing conditions, as extremely moist or dry soils may keep producers from sowing at the optimum planting date.
The largest variability in the progress of area planted in Kansas in the period 1994-2015 occurred between Sept. 20th and Oct. 15th. During the period between these dates, the difference in area planted between the earliest and the latest years between 1194 and 2015 was more than 40% (Figure 4). In other words, while 50% of the wheat area was sown by September 21st in the earliest year on record, only 7% of the area was sown by at the same date in the latest year on record. In the latest year, it was not until Oct. 11th that 50% of the wheat area was sown. The variability in planted area was lower at earlier planting dates (before Sept. 20th), probably because most producers tend to wait until the optimum planting window. Year-to-year variability in planted area also decreased toward the late planting window (after Oct. 15th), as most of the acreage had been planted by that time most years.
Figure 4. Percent wheat area planted in Kansas after September 1st for the earliest and latest years between 1994 and 2015 as reported in the USDA-NASS Crop Progress Reports (https://www.nass.usda.gov/Publications/National_Crop_Progress/). The range in area sown is shown as a light purple area in the main graph. Inset shows the difference in percent area planted between the earliest and the latest sowing years during this time period.
c) How wheat growth can be affected by sowing date
Sowing wheat early: Sowing wheat at an earlier-than-optimal date can result in lush vegetative growth, which will require more water to maintain the canopy later in the growing season. Producers who graze their wheat benefit from this lush growth and are encouraged to plant wheat two or three weeks earlier than the optimal sowing date for grain. Early sowing can also lead to an increased incidence of fall pest infestation, such as Hessian fly, and diseases transmitted by certain vectors more active in warmer temperatures, such as wheat streak mosaic (transmitted by wheat curl mites) and barley yellow dwarf (transmitted by bird cherry-oat aphids and greenbugs). The consequences of an earlier-than-optimal sowing date are discussed in a previous eUpdate article, available here.
Sowing wheat at the optimal time: The optimal sowing time differs year-to-year due to environmental conditions, such as temperature and precipitation, but the optimal winter wheat sowing range for different regions in Kansas is shown in Figure 1. Sowing wheat at the optimal time usually stimulates the right amount of fall tiller formation as well as root development to optimize yields while avoiding a lush vegetative growth. Fall-formed tillers contribute more to yield potential than spring-formed tillers. Therefore, it is crucial that about 3 to 5 tillers are well established before the winter sets in. Additionally, this tiller formation combined with a good crown root system development prior to winter dormancy increase winter hardiness of the crop, and consequently the chances of winter survival.
Sowing wheat late: Many reasons may lead producers to plant wheat late. Double-cropping wheat following a late-harvested summer crop, such as soybean or sorghum, is common in many regions of Kansas. Delayed planting date due to environmental conditions, such as soils that are too dry or too wet, may also occur. This year, many producers in central and eastern Kansas may face a delay in planting date due to wet soils (please see accompanying article in this issue of the Agronomy eUpdate, “Wheat planting conditions as of mid-September 2016”). When wheat is sown past the optimal window, it is generally sown into colder soils and the crop is exposed to cooler air temperatures. Sowing into colder soils will delay wheat emergence, so the importance of a seed fungicide treatment increases as planting date is delayed. Additionally, the crop will experience decreased fall tiller formation because wheat development is dependent on temperatures (Figure 4). Thus, increasing seeding rates in these circumstances is also warranted.
Figure 5. Difference in fall growth as a consequence of planting date following summer crops. Photos were taken December 8, 2015 from neighboring fields. One field was sown in early October no-till following corn (left); the other field was sown in late October no-till following soybeans (right). Photos by Romulo Lollato, K-State Research and Extension.
- Seeding rates
Optimum seeding rate varies with geographical location in Kansas, following the precipitation gradient (Figure 5). If sown at the optimal date, the optimum seeding rate should be about 1,125,000 - 1,350,000 seeds per acre in the eastern portion of the state, where annual precipitation is more than 30 inches, or under irrigated conditions. The seeding rate should be decreased to 900,000 - 1,250,000 seeds/acre in the central region, where annual precipitation ranges between 20 and 30 inches; and a further decrease in seeding rate should occur in the western third of the state where annual precipitation is less than 20 inches, for a final seeding rate between 750,000 and 900,000 seeds per acre in that region.
Seeding rate should always be discussed along with planting date, and in many times with soil fertility status as well. As mentioned above, later planting dates will decrease the potential number of fall tillers formed and grain yield will be more dependent on the main stem along with maybe one or two tillers formed during the fall. Thus, the seeding rate should be increased as planting date is delayed (more information provided here). On the other hand, producers with a history of manure application and very high soil phosphorus and organic matter levels have been observing a yield increase from reduced plant populations. The reason behind this response is that high phosphorus levels and increased overall fertility resultant from long-term application of manure can increases the wheat tillering potential, decreasing the need for high plant populations.
Figure 6. Optimum planting rates for winter wheat in Kansas. Figure adapted from K-State Research and Extension publication L-818, Kansas Crop Planting Guide.
Romulo Lollato, Wheat and Forages Specialist
lollato@ksu.edu
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