Caution for Sowing Wheat in Hot Soil

August 11, 2011 09:56 PM
 

By Jeff Edwards, Oklahoma State University Extension, jeff.edwards@okstate.edu  

Short or nonexistent pastures and tight hay supplies mean that producers will be anxious to get wheat pasture going as soon as possible. Wheat can be sown for pasture as mid-August in Oklahoma, but there are a few cautionary items to consider prior to sowing wheat this early.
 

Is there enough moisture to sustain the crop?

It is important to remember that having enough moisture to get a crop emerged and having enough moisture to sustain wheat forage throughout the fall are two different things. An early---sown (prior to Sept. 15) wheat crop will quickly establish a dense crop canopy that will quickly exhaust moisture reserves. If forage is in desperate need and forage is the only consideration, this might be an acceptable scenario; however, if there are plans to harvest grain next spring or to sustain season---long forage production, then delaying planting until mid-September will help stretch soil moisture a little farther.
 

Will you have to plant deep to reach moisture?

That first structure protruding from a germinating wheat seed is actually not a leaf. It is the coleoptile. The wheat coleoptile is a rigid structure whose sole purpose is to “punch through” the soil surface so that the first true leaf emerges above the soil surface. If this does not happen, the first true leaf will try to extend below the soil surface, turn yellow, and take on an accordion---like appearance.
 
Modern semi---dwarf wheat varieties have shorter coleoptiles than older, tall wheat varieties and coleoptile length is shortened even further by hot soil conditions. So it is important to plant a variety with a longer coleoptile length (e.g. Doans) if planting deeply into hot soils. A rating of coleoptile lengths for wheat varieties can be found in OSU Fact Sheet 2141 OSU Wheat Variety Comparison Chart.
 

Is the variety high temperature germination sensitive?

High temperature germination sensitivity is a fancy way of saying that some wheat varieties simply don’t germinate well in hot soil conditions (e.g. 2174, Overley). The extent of the sensitivity varies by year so Overley might germinate fine in 95F soils one year and produce a 10% stand in the same soil conditions the next.
 
When sowing early, it is best to avoid varieties that have high temperature germination August 3, 2011 2 sensitivity (e.g. Duster, Endurance, or Armour). Soil conditions generally cool due to lower ambient temperatures or cooling rains by about September 20; however nothing seems to be “normal” this year so it is best to know the level of germination sensitivity in the variety you are planting.
 
A rating of high temperature germination sensitivity for wheat varieties can be found in the variety comparison chart linked on the previous page. A more detailed explanation of the phenomenon can be found in OSU Fact Sheet PSS 2256 Factors affecting wheat germination and stand establishment in hot soils.

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