nitrogen fixers ... roots excretions benifical?

bigeasyjock(z8Ms)August 14, 2005

My question concerns growing nitrogen fixings plants. I have been given conflicting info as to wheter or not 'living' nitrogen fixing plants benifit the soil. I do understand that with the pea vine once you have killed the plant and turned it under the rotting plant and roots release the stored nitrogen. But does a living plant, I'm thinking wax myrtle, increase the soils nitrogen levels? If I was to top these bushes, thus killing off root mass due to lack of greenery to support the roots, those roots that died off will release nitrogen to the soil correct?

I just trying to get a handle on how to best use nitrogen fixing plants. I would perfer to use permanent bushes like the wax myrtle which is a self seeding (think weed).


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taxonomist(7b VA)

I believe that you will find some very interesting information relating to your query in the publication PLANT PHYSIOLOGY by Taiz and Zeiger, 1998,pages 324-333.If this is not readily available, perhaps your local library can order a copy of the article.I would send you a copy myself, but I don't know how to do it. I'm a real dumbo in computer technology.
Good Luck!

    Bookmark   August 18, 2005 at 7:42PM
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Peanuts are good Nitrogen fixers.

    Bookmark   August 19, 2005 at 9:28AM
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Thanks for the replies.

I'll try to find that article next chance I get a crack at a real libary. Can you give me the gist of what it says?

Chaman I can list ya a couple dozen N fixers though I admit I didn't know about peanuts. The question is must the plant be killed in order for the accumulated N to be released from storage within the roots, like one would do with legumes, or if N fixers release that converted free atmospheric N through their roots to the surrounding soil even while living.

I've a LSU professor friend who says no they don't. I've also read that with the legumes not only does the plant need to be killed but must die before seed production or the N will find up in the seed and not in the roots.

This is an important aspect of Permaculture that I'm getting mixed answers on. If living N fixers do not release N into the surrounding soils than planting a permanent N fixer, such as a wax myrtle, makes no sense other than as a part of the succesion of a plant community.
One final though has to do with kill back. Using the wax myrtle, if I was to wack the plant back by a 1/3 will a like amount of root die off occur? Seems that this root die off would release N to the soil for sure. Also the limbs would act as a compostable too. With this method I would plant the myrtle with say an apple tree. Once or twice a year I would cut back the myrtle releasing N to the soil for the apple tree to use.

So you see its important to determine if the myrtle's roots releases N to the soil during normal growth. If it does than this hedging back of the wax myrtle is not needed.


    Bookmark   August 22, 2005 at 7:31PM
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Peanuts are legumes too.They will fix the Nitrogen thru nodules on the roots.It is possible to keep the roots in the soil for other legumes after harvesting.For peanuts we throw the plants and roots back in the soil and plough it after harvesting.

    Bookmark   August 24, 2005 at 4:25PM
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just_curious(7b/8a Canada)

I kill clover all the time, and my guess is that it only release nitrogen from the roots after it is dead.

    Bookmark   August 26, 2005 at 11:21PM
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weebus(Z8 Sunset 5 WA)

You could do some root pruning, take the roots that you trimmed off, put them in a blender, with H2O and make a liquid of it all. Pour them back on the soil you want more nitrogen in. You wouldn't have to sacrifice a plant to do some nitrogen fixing...

    Bookmark   August 28, 2005 at 1:58AM
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albert_135(Sunset 2 or 3)

When I took high school agriculture, back there back then it was required for boys, I was taught that the legume had to be tilled back into the soil before blooming for it to be a worthwhile soil improvement.

Farmers and ag teachers were not as dumb as their reputations but they did sometimes do things because of untested folk wisdom.

    Bookmark   August 29, 2005 at 1:08PM
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albert has made a good point about legumes.
This was done frequently at the time when modern fertilizers were not readily available.Tender Nitrogen fixing plants were grown earlier and ploughed back in the soil before planting the main crop. These young plants will be rich in Nitrogen, will quickly bio-degrade in the soil once ploughed.
I have seen my Dad ploughing Gour bean plants before planting new crops.He used Guar or Cluster bean plants for the purpose. Guar beans are easy to grow and reach usable height quickly.
Guar beans are used in manufacturing Explosives which suggest that they may be rich in Nitrogen along with other good things for applications.

    Bookmark   August 30, 2005 at 8:29AM
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the N fixers are not the plants, but the bacteria that live in the roots of these plants. These roots and bacteria live in symbiosis. The bacteria provide fixed N to their host plant, since they are living inside/around its roots.
Once you seperate shoots from roots, the bacteria will keep on fixing N for a while and eventually either go dormant or die, since they can no longer benefit from the nutrients that they were getting from their host plant.
Those roots at this point will contain high levels of N.
I am with weebus on this one, you don't need to sacrifice a whole plant, some pruning will do the job.
Now, to the question wether or not other plants benefit from these bacteria, I would say it depends on many things : how the roots of the 2 plants interact together, how big the colonization is, how much N is available, etc. Probably they do get some benefits, but not as much as the host plant itself.
For Plant Physiology Journal : articles older than one year are viewable by everyone, just click on the link below, it will take you to their website.

Here is a link that might be useful: Plant Physiology Journal

    Bookmark   September 10, 2005 at 11:28AM
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Ploughing back tender Guar plants will provide Nitrogen from the root nodules and the green leafy part will provide mulch to the soil.So will happen with other Legumes too.
I grow clovers all around four borders of my plot and use them as mulch.Just before the plants start flowering some of them are pulled out and thrown over weedy ares along with grass clippings.This makes it easier to remove weeds.

    Bookmark   September 12, 2005 at 9:06AM
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pinetree30(Sierra Westside)

Roots of alders, which unlike legumes have nodules inhabited by Frankia, leak nitrogenous substances. Also, rainfall that washes over the foliage leaches nitrogen. So the trees don't have to die to contribute nitrogen to their environment.

    Bookmark   November 1, 2005 at 11:53PM
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whitejade(z5 MI)

I posed a question like what I think you are asking on another forum ( living nitrogen fixing plants enrich the plants around them?) and someone did write that they had seen research which suggested that this is indeed the case..that the grass growing around the nitrogen fixing plnats had gotten quite a bit of its nitrogen from those leguminous plants , probably through close root interaction in the soil. So you can dig them in or you can allow them to stand ...and in all ways it seems that nitrogen fixing plants do valuable things.

I cannot recall which forum it was that this thread was on, likely Soils. If you go there and type into that search engine "Do I have to dig in my Clovers" or something like that you should see it.

    Bookmark   November 2, 2005 at 8:00AM
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'Root exudates as mediators of mineral acquisition in low- nutrient environments.' Felix D.Dakota; Donald A.Phillips
Plant and Soil 245:35-47;(2002)
available online @ >> 'Mineral Deficiency' > 'Updates'...
also cross reference citations using journal site search engines...or keywords

Here is a link that might be useful: plantstress site

    Bookmark   November 2, 2005 at 9:59AM
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White jade that was indeed what I meant but didn't state the question as clearly as you had done. '.... enrich the plants around them?" Thats what I was thinking especially while still living members of that plant community. I'll go digging around the soil forum (pun intended ;o)
But first let me go see what Pickwick's link is all about.

    Bookmark   November 5, 2005 at 7:51PM
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Holy Cow Pickwick thats one sweet site!!!!! I'll be rootin' around there for a good while I can already tell ya!!!!
Thanks Mike

    Bookmark   November 5, 2005 at 7:54PM
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keking(z6 TN)

When I was a youngster, I sometimes killed time in summer by looking for 4-leaf clovers. There was a patch that usually had one or two whenever I got the urge to look. When school started again, I made a mental note of the location of my favorite patch so I could return to it the following year.

Summer came again, but there was no clover at all in the spot I remembered. Not one leaf. The spot was covered with grass. A few feet away was a patch of clover that had not been there the previous year.

I finally figured it out. Clover enriched the soil with nitrogen by hosting nitrogen-fixing bacteria. The richer soil allowed grass to crowd out the clover. And where grass had depleted the nitrogen the previous year, clover moved in because it "rolls its own" nitrogen.

Taking in the big picture (over time), plants that host nitrogen-fixing bacteria share the wealth with other species.


    Bookmark   May 31, 2012 at 12:15PM
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leftwood(z4a MN)

A whole patch of clover was completely (and naturally) crowded out by grass in just one season? I don't see how that could be possible.

    Bookmark   July 27, 2012 at 10:22AM
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albert_135(Sunset 2 or 3)

A whole patch of clover was completely (and naturally) crowded out by grass in just one season? I don't see how that could be possible.

This was commonplace where I grew up.

    Bookmark   July 30, 2012 at 2:40PM
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