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Scouting Soybean (06/27/19)

Soybean plants have the ability to form a symbiotic relationship with nitrogen-fixing Rhizobia bacteria, resulting in the formation of nodules.

Nodulation

Soybean plants have the ability to form a symbiotic relationship with nitrogen-fixing Rhizobia bacteria, resulting in the formation of nodules. At this time of the year, the soybean plants are developing rapidly, and nodules started to develop shortly after plants emerged. If the plant is around 6 inches tall with the first or second true leaves (trifoliolate leaves) unfolded, bacteria in the nodules will start fixing Nitrogen gas into plant available N. The number of nodules will increase until about the R5 (the beginning of the seed formation). To check for nodulation, dig up a plant, wash the roots in a small bucket of water, and observe the presence or absence of nodules on the root. To check the activity of the nodule, cut the nodule open and see if the color is pink or reddish, indicating appropriate functioning of the nodule.

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Iron Deficiency Chlorosis

Driving around the countryside some of the soybeans fields are starting to show a yellowing, caused by iron deficiency chlorosis (IDC) of soybean plants. The unifoliate leaves of soybeans are usually green, as they can utilize the iron present in the seed. As the trifoliolate leaves start to develop, chlorosis often starts to appear when soybeans are grown on high pH soils with free bi-carbonate and poorly drained regions of the field. The deficiency appears first on the youngest leaves. Under severe conditions, the growing point is injured, and recovery is limited, resulting in a reduced soybean yield. It is important to note the IDC tolerance level of the soybean variety in the affected field and in the future, plant varieties with more tolerance in fields with severe IDC expression.

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Hans Kandel

Extension Agronomist Broadleaf Crops

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