Crop Emergence Concerns | Crop Update

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Crop Update: May 5, 2020
By Eric Yoder
Crop Emergence Concerns....
 
While #Plant2020 appears to be going much better than last year, Mother Nature always has some curves in store for us. Some seeds have already endured snowfall, variable temperatures and prolonged germination, just to name a few. On the other hand, lots of soybean acres were planted earlier than normal this season as the conditions allowed. So how will this all play out as some soybeans are starting to emerge and the forecast for Friday night will be at or below 32 degrees in several areas of the Midwest? Below you will find 2 good articles discussing what impacts these chilly temps could have on newly planted or emerged corn and soybean seed.   
Excerpt below regarding cold temps on emerged soybean seedlings
First of all, 34F will not impact above-ground tissue.
Second, tissue freezing does not even take place at 32F because cell cytoplasm has solutes in it – like a modest anti-freeze, which depresses freezing point of the tissue a degree or two less than 32F – thus air temps surrounding the tissue have to get to below 31 or 30F before tissue freezing can occur.
Third, the soil surface is typically warmer than the air temperature (particularly when the soil is wet) and does not give up heat acquired during a sunny day as fast as the air does after sunset. In actuality, the interface between soil surface temp and the air temp near that soil surface will be closer to the soil temp than to the air temp which most peopled measure on thermometers viewable at their height (not at ground level). Biophysically, control of the soil temp over the air temp this is called the “boundary layer effect”). So don’t trust air temperatures read on thermometers unless you know what the air temperature near the soil surface was (put a thermometer on the soil surface tonight where the cotyledons are and check it just before dawn (when the soil surface temp reaches its nadir for a 24-hour temperature cycle) and send out an e-mail blog to your producer colleagues early the next day.
Fourth, the cotyledons are a huge mass of tissue that are about 95% water. That big amount of water-filled tissue is hard to freeze unless the exposure to temps of 30F at the soil-air interface is many, many hours. Cotyledons will freeze faster (in fewer hours) but only if the soil surface temps get well below 30F (say 25F). The only concern I would have is when cotyledons are no longer closed and protecting the young stem tip. However, if that is in fact frozen off, the nodes to which the cotyledons are attached will regenerate TWO main stem tips. Not an ideal way to start the growing season, but better than having to replant (0.5 bu/ac loss per each day that soybeans are NOT in the ground on May 1).
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