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Drought Effect On Corn and Soybean and Alternative Management Considerations

By Mark Licht and Zach Clemens

Low rainfall and high temperatures recently have caused some drought stress on local crops this summer. This is not wholly unexpected and there are some strategies crop producers can do to minimize the damage.

Higher nighttime temperatures cause plants to have higher nighttime respiration which in turn uses up sugars produced through daytime photosynthesis. Additionally, higher nighttime temperature speed up the number of heat units accumulated per day and lead to a faster grain filling period and earlier maturity.

A lack of moisture reduces corn biomass production by reducing cell expansion. Because corn silks have a very high water content, this stress could cause a delay in silk elongation. Slower or delayed silk elongation can result in asynchrony of pollen shed and silk receptivity (ie, silks emerge after pollen shed in most severe cases). The overall result is that poor pollination will occur due to the dry conditions. If these factors continue through pollination, kernel abortion will occur, causing exaggerated tipping back. Typically, tip back can occur into the blister stage but under most severe conditions tip back or kernel chips can result into the milk stage.

Drought conditions can result in soybean flowering to stop and even pod abortion. If weather conditions improve, flowering will re-initiate into the early seed filling stage and pod setting can occur into mid seed filling stage. Hence, rains in August can really benefit soybean yields.

Yield Estimates

Yield estimates on both corn and soybean are needed to make good decisions regarding harvest, storage and marketing decisions. While making estimates are straight forward:

Corn yield=earsacre*kernel rowsear*kernelsrowkernels per bushel

Soybean yield=plantsacre*podsplant*seedspodseedspound*60poundsbushel

It is extremely important to factor in adjustments because of drought. The critical assessment in stress years is to adjust for seed weight. For example, 90,000 kernels per bushel is the typical estimate in non-stress conditions. However, in stress conditions, this should be adjusted to 105,000 or more kernels per bushel. And 2,600 beans per pound should be increased to 2,900 or more.

Cover Crops

It is a good idea to plant cover crops following drought stressed corn or soybean for a few reasons. Cover crops will protect the soil and minimize the amount of soil water evaporation that occurs. Cover crops also help with flushing of accumulated nitrates if/when rainfall comes. To be successful with cover crop establishment in dry conditions, stick with cereal rye (winter hardy ahead of soybean or oats (winter kill) ahead of corn. This approach will limit water use in the spring which could be important if drought conditions continue through the winter. Soybean can withstand dryer conditions than corn plus allows more time for spring termination decisions to be made. And try to aerial, broadcast or drill seed ahead of forecasted rains and use the standard seeding rates.


Seeding cover crops in dry conditions


First, be aware that drought conditions also are conducive for field fires. Make sure equipment is working properly and take precautions to avoid field fires. Ensure that combine settings are adjusted to account for smaller seed size, lighter seed weight and smaller stem/stalk diameters. Remember that grain lost in the field whether because of combine head loss or spread out the back of the combine can be problematic the following year.

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