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Legumes and Soil Mycorrhizae

By   /  October 7, 2013  /  6 Comments

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We all appreciate legumes and their marvelous ability to fix atmospheric nitrogen and release it int
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About the author

Dave Scott is a Livestock Specialist with the National Center for Appropriate Technology (NCAT). Dave has 30 years experience with intensive grazing, including dairy and sheep. He has also served as a part-time consultant in management-intensive grazing, helping ranchers design and implement grazing systems that increased their stocking rates and net profits. Currently, Dave and his wife, Jenny, operate Montana Highland Lamb, a 200-ewe enterprise that markets over 50% of their grass-based natural lamb directly to the consumers in southwest Montana.


  1. Paul Cereghino says:

    I am suspecting that our focus on direct mechanisms might weaken our ability to manage complex systems like the messy soil/plant world. Once nitrogen gets into the plant, there are lots of different ways it gets into the soil food web. It seems likely that this years soil activity is feeding off of last years nitrogen fixation. I seem to remember cases where nutrient transfer from plant to plant appear to be mediated by a fungi (using isotope tracers? I’ll have to look that up again sometime). I haven’t seen any substantive research on fungi-to-fungi exchange, and it makes my brain hurt to figure out how to isolate those mechanisms for observation.

    Perhaps the larger consideration is about how fertilizer costs are tied to fossil fuel costs, and so developing self-sustaining soil systems might be about more than whether you are into fungi.

  2. bill elkins says:

    Dave -We’ve long known that legumes carry symbiotic N2 fixing bacteria in root nodules, and your post indicates that these bugs release their fixed nitrogen to microrhizae which then pass these compounds back to the plant. That begs the question whether mycorrhizae associated with legumes are functionally the same as those associated with roots of other plants (grasses) in the same location? Or are grasses fed by different mycorrhizae? I assume mycorhizae are biodiverse, right?

    • Dave Scott says:

      Hi, Bill,
      Good questions! I do not know the answers. Remember, I am a farmer! The soil community is so diverse and nutrient pathways so complex I would not be surprised about any configuration. Just think of the zillion times of species that are below ground vs. those above ground!

      I have not read anything concerning this specifically. It is a very interesting question. I will try and find out an answer to it.
      Give me some time and I will get back to you through On Pasture.

      Thank you very much for your comment and for reading On Pasture. I hope you have enjoyed my articles on intensive grazing!

      Yours, Dave Scott

      • Dave Scott says:

        Howdy, Bill and Paul,
        A search through google scholar shed some light on this question. It seems that one species of micorrrhyzae can transport N from a legume to a grass.

        Please see this reference:

        Yours, Dave Scott

        Of course, it does state that additional study is needed!

        • bill elkins says:

          Dave- You are a veritable human Google to come up with that link so fast! It does answer my question quite well enough for now, so thanks!
          But you lay yourself open to getting pestered- here’s another one. You wrote that you were considring experimenting with mycorrhizal extracts. Have you percived a shortage of MRF in your soil? How would one begin to assess that? I am aware that Elaine Ingham’s Soil Foodweb Co. deals with such questions., but have not tried her yet. There may be other ways to look.cheers, B.

          • Dave Scott says:

            Hi, Bill,
            Yes, we did test our soil with Earthfort’s biological analysis. Earthfort (just Google) bought Soil Food Web and is doing business. The contact there is Matt. Our soil tested low in active fungi. This is what led me to consider the mycorrhizal extracts.

            Yours, Dave

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