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Causes of yellowing soybeans

Audrey Kittrell 06/29/2011 @ 5:04pm Editorial Intern for Successful Farming magazine and Agriculture Online

Corn isn’t the only crop that’s turning fields yellow right now.  A number of soybean fields are showing a slight yellowing of leaves, and may need additional fertilization, according to Fabian Fernandez, University of Illinois Extension specialist in soil fertility and plant nutrition.

This time of year if soybeans are showing signs of yellowing, it is likely the result of stressful growth conditions.  “Many soybean fields are starting a rapid shoot growth phase.  Meanwhile, the root system, which in some instances has not developed very well, is not yet able to meet the increasing nutrient demands, causing what is likely a temporary nutrient deficiency,” Fernandez said.

Wet soil conditions

The wetter-than-normal soil conditions are to blame again—this time for unhealthy soybeans.  Water is critical for dissolving nutrients and transporting them to the soybean plant, but in excess, it can block other important processes.

“Temporary nutrient deficiencies can be observed when excess water in the soil depletes oxygen and builds up carbon dioxide levels.  Although oxygen is needed by roots to grow and take up nutrients, high carbon dioxide levels are toxic and limit root growth and activity,” Fernandez said.

Low sunlight conditions usually occur with wet soil conditions, which further exacerbate the health of soybeans.  Clouds reduce photosynthetic rates and nutrient uptake by the crop.

Dry soil conditions

The opposite condition—dry weather—can have similar negative effects on soybean health, although it is not as much of an issue this year.  Fernandez says when the surface layer of the soil is too dry, the root system of the plant is small and shallow, and limits nutrient movement to the rest of the plant.

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