Amanda de Oliveira Silva, Small Grains Extension Specialist
I feel like this year’s planting season started like “Hurry up and wait! ” as my colleague Gary Strickland would say.
We had a great start with dual purpose wheat planting. There were lots of drills rolling around the state, and we were able to plant our dual-purpose trials in good soil moisture at 1 to 1.5 inches deep. However, with the wind blowing hard, temperature in the 80-90’s in some days, and lack of rain in the past few weeks, the soil has been drying up quickly in many areas of the state. There is a small or no chance of rain in the forecast for the next two-three weeks, and I am hearing producers discuss whether to park their drill for now or dust in wheat.
According to Wes Lee, the Oklahoma Mesonet Ag coordinator, rainfall is going to be very limited unless one of the tropical storms moves further west than expected. Dewpoints are very low, so if a rain occurs it will be light. He also mentioned that our current situation is a result of the moderate La Nina ENSO pattern, which tends to bring the driest falls and winters to Oklahoma. Gary McManaus, the Oklahoma Mesonet State Climatologist, says that predictions are not favorable at this moment, and we will likely see drought development and intensification by the end of the month and year in Oklahoma.
As of October 4th, 45% of Oklahoma wheat was already planted and 20% emerged, which is about the same as the 5-year average (USDA-NASS, 2020). They also reported that we are 54% short and 34% adequate in topsoil moisture, and 33% short and 56% adequate in subsoil moisture. Figure 1 shows the 4” plant available water in the soil at this time of the year for 2019 and this year.
With a likely drought scenario for fall and dry conditions advancing quickly in our state, it is good to have in mind the possible effects of drought on the wheat germination and early growth.
Wheat germination and emergence in dry soils
The most important physiological requirement for wheat to germinate and sustain the developing seedling is soil water. Therefore, planting decisions needs to be based on a combination of available soil moisture and expected rainfall. In addition, other factors such as adequate seeding depth, sowing date, soil fertility, seed treatment, seed quality, etc. should be considered to guarantee a good crop establishment. For more information, check our previous blog post (planting-date-and-seeding-rate-considerations-for-winter-wheat) and the materials on our website.
Wheat seeds need a minimum water content of 35 to 45 % of its dry weight to initiate germination, and germination will increase as moisture levels increase. Dry soils can still have a relative humidity of 99%, and that can be enough moisture for seeds to germinate, it might just take longer than if it were in moist conditions. My concern with the current situation in Oklahoma, is the lack of rain in the forecast. This could result in enough moisture to start the germination process in certain areas of the state, but the seedling emergence and growth could be compromised if we don’t see any rain soon.
What happens if the soil completely dries out before wheat emergence?
There are three phases during the germination process; water absorption, activation for when the seed coat is ruptured, and visible germination for when the radicle emerges, followed by the seminal roots and coleoptile. These processes will start and stop depending on the soil moisture. Thus, if the soil dries out before the roots and shoots are visible, the seed remain viable and the germination will be paused and continue once water is available. However, if the soil dries out after those structures are emerged (approximately 4-5 days after germination has begun), the seedling may not tolerate the lack of water resulting in loss or incomplete stand.
What should I do then? Choose your battle!
The optimal time for planting wheat in a grain-only system in Oklahoma is around Mid-October. So, I would say we still have a week of wiggle room to decide what do. There are different ways we can go about it, but we must keep in mind that there is always risk involved when planting wheat in dry conditions.
If you decide to dust in your wheat and wait for rain for wheat to germinate, watch your seeding depth. The optimum seeding depth to plant wheat is about 1-1.5” deep. We typically don’t have as many issues with winterkill in Oklahoma as they do in more northern states, so I am comfortable with dusting in at about 0.75 – 1” deep. Planting at 0.5” or less is too shallow in most circumstances. Also, there is always a chance for pounding rain occurring and forming soil crusts which makes it difficult for the coleoptile to push through the soil surface and may result in poor emergence. Fields with stubble cover may be less affected by pounding rain and reduce the risks of soil crusts forming. If the forecast follows through, and we receive rain in the next weeks, it would be light, and that could cause wheat to emerge but may be not enough for wheat to continue growing. Most of the field I visited in the past days had good subsoil moisture, so that could help!
If you decide to plant deeper to reach moisture, be careful with the coleoptile length of the variety you have, and make sure it has a long-enough coleoptile that will allow emergence if conditions are favorable. Consider increasing seeding rate to compensate for the low emergence which is prone to occur in this situation.
Should we wait for rain to plant then? This is a farm by farm call and it depends on which source of risk you find most comfortable. Personally, I would rather plant my wheat in the optimal planting window and adequate seeding depth than waiting for a rain that may take too long to happen or missing my optimal planting window. If the latter is the case, make sure to bump your seeding rate to try to compensate for the reduced time for tillering. Planting wheat at optimal time allows for more time for root growth in seedlings, helping the crop to have a quicker establishment under dry conditions and possibly help the plant to scavenge for water that is available deeper in the soil profile.
Are there any specific agronomic traits that could help wheat seedling growth under water stress?
Traits that could help with seedling growth in dry conditions are the coleoptile length, which allows to plant a little deeper in moisture and good emergence (if deep planting is the practice of your choice). There are indications that sowing wheat varieties with larger seed may help to reduce the negative effects of drought during early growth (Mian and Nafziger, 1994). In general, the greater reserve of larger seeds results in a faster germination and crop establishment by increasing root growth and tiller production. Although, there are varieties with small seed size that germinate better than larger seeded varieties, demonstrating that genetics can also play an important role on the ability of variety to germinate in dry soils.
Wheat is known to be a resilient crop and to adapt to the low soil water availability, wheat that has already emerged will try to reduce transpiration (i.e. water losses from leaves) by reducing tillering and forage production.
Summary for managing wheat in dry conditions
Planting options: Dust in wheat at 0.75 – 1” deep, plant deeper to reach moisture, or just wait for a possible rain
Optimal timing for planting grain-only systems is Mid-October
Increase seeding rate if planting later than the optimal time
Plant varieties with long coleoptile length if planting deeper to reach moisture
There is no need for additional N in the fall as crops will not be using N in dry conditions
Don’t hesitate to contact your County Extension office.
For references cited in this post and additional information, see below:
GRDC. Grain Research and Development Corporation, Australia. 2016. Wheat – Plant growth and physiology. https://grdc.com.au/__data/assets/pdf_file/0026/370673/GrowNote-Wheat-North-04-Physiology.pdf
Lollato R. and Holman J. 2020. Considerations when planting wheat into dry soil. K-State Agronomy eUpdate – Issue 821. https://eupdate.agronomy.ksu.edu/article_new/considerations-when-planting-wheat-into-dry-soil-409
Mesonet Oklahoma http://www.mesonet.org/index.php/forecast/local_and_regional
Mian and Nafziger, 1994. Seed Size and Water Potential Effects on Germination and Seedling Growth of Winter Wheat. Crop Science. 34(1), 169-171. https://doi.org/10.2135/cropsci1994.0011183X003400010030x
Shroyer J.P., Kok H., and Thompson C.R. Planting Practices in Wheat Production Handbook. K-State C529. https://bookstore.ksre.ksu.edu/pubs/c529.pdf.
USDA-NASS, 2020. Oklahoma Crop Progress and Condition. October 5, 2020. https://www.nass.usda.gov/Statistics_by_State/Oklahoma/Publications/Crop_Progress_&_Condition/2020/ok-cw-10-04-2020.