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Soybean Root Nodules (07/24/14)

With the right kind of Rhizobia bacteria, nodules may form on the soybean roots. With this symbiotic relationship between the bacteria and the soybean plant, nitrogen gas is fixed into a plant-available nitrogen form.

Soybean Root Nodules

With the right kind of Rhizobia bacteria,plsc.kandel.1.soybean root nodules nodules may form on the soybean roots. With this symbiotic relationship between the bacteria and the soybean plant, nitrogen gas is fixed into a plant-available nitrogen form. Without the proper bacteria, the plant will not have nodules and the soybean plant will depend on soil-available nitrogen for its growth and development. Without the nodulation, the soybean plant may not be dark green and the yield may be lower than expected. Fields without a soybean history are the most likely fields to show the light green soybean plants. Even if the seed was inoculated with the right bacteria it does not guarantee that nodules will develop. If adverse conditions occurred between the time of inoculation and planting (for instance long storage of the inoculated seed under warm conditions) the bacteria may not have been viable. There can also be field conditions after seeding which inhibit nodulation, for instance saturated soils or very dry soils conditions. It is possible to have nodulation in certain parts of the field and not in the stressed areas. Dig up some plants which appear light green, with a spade (pulling them out may dislodge nodules) and wash the roots in a bucket of water. Observe if the plant has root nodules. Cut a few nodules open and look at the color. Pinkish inside color of the nodules indicates healthy nodules. If no root nodules are found in an area of the field make sure fresh soybean inoculant is used whenever soybeans are planted again in the same field.

Hans Kandel

Extension Agronomist Broadleaf Crops

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