Root nodules

David W. Kramer kramer.8 at
Fri Oct 5 09:34:15 EST 2001

>Hi, all!
>I've been trying to grow clover, soybean, etc. to show root nodules to
>students without success.  Can anyone recommend a plant that does well
>and what is the amount of time needed to grow these plants from seeds in
>order to see root nodules?  I've been using the rhizobium innoculum from
>Carolina Biological... it's a black dust.
>Kathy Pelkki
>pelkki at
There is a good possibility that the inoculum has gone past its effective
date.  Here are some things we've learned from a soybean experiment in our
Plant Biology 102 lab:

1.  Use the freshest inoculant you can find.  I get it from a local farm
supply store and they provide it free of charge when they learn that it is
for an experiment at OSU!  They don't receive a fresh shipment until about
April here in Ohio (just in time for soybean planting).  Close the plastic
bag very tightly and store the inoculant in the refrigerator.  You might
want to put the bag in a jar for added protection.  Even so, its
effectiveness falls off rapidly.

2.  Wet the seeds then roll them in the inoculant.  To be sure there is
sufficient inoculant, we sprinkle some in the planting hole, on top of the
seed, before covering it with soil.

3.  Use a soil that has little or no nitrogen.  If there is an ample supply
of available nitrogen (nitrate, etc.), the soybeans will block entry to the
bacteria.  (Why feed the bacteria when you don't need them for nitrogen
fixation?!)  We use ProMix soil which has no fertilizer.

4.  When looking for nodules, look at the transition zone between root and
stem.  In our experience, the nodules form very high on the root system,
not on the finer divisions of the root.

Good luck!

David W. Kramer, Ph.D.
Asst. Prof. of Evolution, Ecology, and Organismal Biology
Ohio State University at Mansfield
1680 University Drive
Mansfield, OH  44906-1547
Phone:  (419) 755-4344      FAX:  (419) 755-4367
e-mail:  kramer.8 at


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