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Soybean Nodulation (6/21/12)

After the second or third trifoliate has emerged it is a good time to evaluate the nodulation of the soybean plants (Figure 1). When the nodules are cut open they should have a healthy pink to red color on the inside.

Soybean plantImportant factors that affect nodulation are the viability of the inoculum (the number of rhizobium bacteria that were placed on the seed), available soybean specific bacteria in the soil, and the soil root accessible nitrogen level. The viability of the soybean inoculum depends on storage time (shelf life of the inoculum) and storage conditions (hot conditions will kill bacteria). Commercial inoculum packaging will list the expiration date for the inoculum. Inoculum is also easily killed by direct sunlight so exposure of inoculated seed to sunlight or excessive heat should be avoided. When digging up the soybean plants the nodules should be readily visible (Figure 2). Nodulation may be limited if dry conditions or excessive moisture saturating the soil followed planting the soybean crop.  Nodules may also be limited because of high levels of available soil nitrogen, which leads to lower nodule production. Other stress factors that may lead to lower nodulation Include hail damaged plants, root diseases, or Iron Chlorosis Deficiency symptoms early in the growing season. The Carrington Research Extension Center has conducted research on soybean seed inoculants (Figure 3). The 13-year average shows a significant 2.1 bushel per acre and a 0.9% protein advantage with inoculation compared with the untreated check. The inoculant average for each year includes numerous inoculation treatments and the majority of trials were conducted on ground without prior soybean production.Nodulation on soybean plant

Soybean chart

Hans Kandel

Ext. Agronomist Broadleaf Crops

hans.kandel@ndsu.edu

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