Ag Instructor Vic Martin: Grain Yield and Cold

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Great Bend Tribune
Published September 13, 2020

The Drought Monitor shows little change from last week, however, the dry/droughty areas have retreated a bit towards the Colorado border.  The forecast is from the previous Tuesday so this doesn’t reflect recent rains.  The six to ten day outlook (September 16 to 20) has below normal precipitation and above to below normal temperatures for the state depending where you are.  We are forecasted for slightly above average.  Looking out eight to fourteen days (September 18 to September 24) indicates essentially more of the same. 

Briefly, while we flirted with the thirties for lows, we managed to stay in the forties.  While the cooler temperatures will slow down maturation and drydown for harvest, it shouldn’t have really hurt the corn or milo (as much of it is pretty far along).  It may hurt soybean yields a bit depending on the maturity stage of the plant.  Soybeans will definitely hurry to the finish line when temperatures hit the mid to upper thirties and we were close.  For the cotton just south of here, time will tell but cotton plants definitely didn’t like temperatures in the forties.

  While we didn’t experience freezing temperatures this past week and avoided the mid to low thirties in our area, parts of Northwest Kansas did.  There is always concern over an early freeze or near freezing temperatures early fall and how it may effect yield.  It helps to understand maturity in our fall harvested crops.

  • Corn and grain sorghum (milo) are a bit easier to understand.  After pollination, the embryo develops for a period of time, endosperm reaches a maximum accumulation of contents in the grain and then starts to dry down.  The seed/kernel loses water and eventually will exhibit what is termed a “black layer” at the base of the seed.  This is termed an abscission layer where the plant severed the xylem and the phloem from the seed.  At this stage the seed is physiologically mature, meaning you can plant the seed in the ground and it will germinate and produce a plant.  The seed isn’t ready to harvest as its moisture content at this stage is over thirty percent moisture and has a long way to go before harvest, typically several weeks or more depending on the weather.  Under ideal conditions, seed can lose a percent or so of moisture per day.  The amount of time from planting to physiological maturity varies depending on the maturity rating of the hybrid.  Most, not all, of the corn in our area was past physiological maturity so yield shouldn’t be affected but harvest delayed.  There’s a bit more spread in milo maturity but much of it was at or close to physiological maturity.  And temperatures weren’t cold enough to adversely affect yield.  Again grain drydown is likely slowed down but not a problem unless you are in a hurry to plant wheat.
  • Soybeans are a bit trickier as they bloom for an extended period of time and have pods at various stages of development and they are a more tropical type plant and less able to tolerate cold conditions.  It appears our conditions should have greatly impacted yields.  It is possible that for later planted soybeans not as far along that later developing pods may have been dinged a bit.  But most beans in the area were fairly far along so again things should be okay.
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