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Tissue Sampling and Nodule Counts

Soybean Nodules

What do you do on a beautiful summer day? Well, spend it in a soybean field of course!  I headed up to Delaware County this morning to complete some more fieldwork on the soybean and lime experiment. Since the soybeans were planted late, they are only just reaching the R1/R2 stage. This is the stage where tissue samples and nodule counts are taken.

The tissue samples were the easiest part of the day. The procedure was to cut off the highest, fully-open trifoliate leaf from 20 plants in each rep. This resulted in 60 individual leaves, once the petioles were removed. The samples will then be dried, ground, and sent off to the lab for analysis.

The harder part of the day was the nodule counts on the roots. Soybeans have the ability to fix their own nitrogen with the help of bacteria.  Prior to planting, soybean seeds are inoculated with a bacterium called Rhizobium japonicum.  This symbiotic relationship between the bacterium and the soybean seed allow atmospheric nitrogen to be converted into a usable form for the plant.  The nitrogen fixation begins with the formation of a nodule on the root of a legume.  For the first few weeks, the nodules are inactive. But 2-3 weeks after planting, the nodules become active.  A healthy nodule will be a pinkish-red inside, caused by leghemoglobin.  These nodules will supply most of the needed soybean plant’s nitrogen for the rest of the growth period.

To count nodules, the soybean plants have to be dug up, being careful not to disturb the root system.  Two plants from five different rows in each plot were sampled for the nodule count.  Once the plants were dug up, the dirt was shaken from the roots, dipped in water and then counted.  The nodule counts ranged from zero all the way up to 30+ nodules.

At harvest time, soil samples will be taken as well as yield monitoring. This is done by counting the number of pods per plant and beans per plot.  The beans will also be weighed to determine the dry matter content.  Until that time, the soybean fieldwork will be quiet.  In the meantime, I have a lot of grinding samples and a few soil tests to run. It should be enough to keep me busy!

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