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How long until nitrogen fixers fix nitrogen?

 
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I planted a lot of beans, a hundred or so possibly, around an apple tree  and some comfrey plants where I am creating a new tree guild.  The beans are obviously suffering a nitrogen deficiency, as evidenced by their yellow color and the fact that dumping urine on them for a few days turned them to a nice dark green.  How long until beans and other annual nitrogen fixers (or perennial ones for that matter) fix enough nitrogen for their own use?
 
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Many plants don't really contribute much until they decompose.

The shortest rotation I can think of would be blue green algae or azolla. There are toxicity problems with algae, so better to go with azolla. If you had a way to impound some water with a tarp or something, you could plant it with azolla and be harvesting nitrogen within 10 days. Chicken manure or any other high phosphorus material makes a good starter. During optimal conditions you may need to harvest every 2 or 3 days. That's the fastest turnaround of any cover crop I've heard of.
 
Todd Parr
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I have chicken manure and other sources of nitrogen.  I'm just trying to understand when nitrogen fixers can fix enough nitrogen for their own use, not necessarily for the surrounding plants.  I'm fine with them not contributing nitrogen to the soil until I chop and drop them.  
 
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It isn't the beans themselves that fix nitrogen, it's the bacteria which, if they are present, form a symbiotic association with the roots.  

If the bacteria aren't naturally present in the soil and you didn't inoculate the seed, the beans won't ever fix nitrogen.

Our soil was totally lacking in them when we first moved here and it's taken a few years before we could stop inoculating our seeds.  If we planted without inoculating, we'd have to add pee to the soil.  When we started to inoculate them, they would grow just fine without pee.  These days there seem to be enough of the right bacteria in the soil that we can just plant them and forget about inoculating.

 
Todd Parr
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Burra Maluca wrote:It isn't the beans themselves that fix nitrogen, it's the bacteria which, if they are present, form a symbiotic association with the roots.  

If the bacteria aren't naturally present in the soil and you didn't inoculate the seed, the beans won't ever fix nitrogen.

Our soil was totally lacking in them when we first moved here and it's taken a few years before we could stop inoculating our seeds.  If we planted without inoculating, we'd have to add pee to the soil.  When we started to inoculate them, they would grow just fine without pee.  These days there seem to be enough of the right bacteria in the soil that we can just plant them and forget about inoculating.



Thank you for that, I guess that must be the issue.
 
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It is not the plant itself that fixes nitrogen, legumes have a symbiotic relationship with rhizobacteria. The plant provides the bacteria with sugars and the bacteria fixes nitrogen. Each legume species has a different rhizobacteria species that colonizes the roots. It sounds like the bacteria that can colonize the beans you planted is not present in your soil. You should be able to buy a seed innoculant for the species you planted, if you try adding that to the soil around the beans it might be able to colonize the roots.
Edit: looks like Burra said the same thing while I was typing my reply the first time.
 
Todd Parr
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So what about perennial nitrogen fixers?  I am just hoping the soil has whatever they need?  Or some plants don't need to be inoculated?  I have autumn olive, seaberry, peashrub, ...
 
Leora Laforge
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Todd Parr wrote:So what about perennial nitrogen fixers?  I am just hoping the soil has whatever they need?  Or some plants don't need to be inoculated?  I have autumn olive, seaberry, peashrub, ...



Perrenial nitrogen fixers are better than annuals, they will typically fix more nitrogen in one year than an annual will as they have a root system in place for the whole growing season, esp the beggining.

It might be good to look into native legumes as your soil might be holding onto the right bacteria if it was not been too badly degraded before.

I would suggest that as you plant new legumes, innoculate the seeds for the next few years. Once your soil is healthy enough to hold onto bacteria, and the right bacteria have been introduced you will no longer need to innoculate
 
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A lot of perinneal nitrogen fixers use the same bacteria as beans do - these are the legumes. But others such as the alders use a different bacteria. If you have native nitrogen fixers that are in the legumes family or another then it is likely the bacteria will get there on their own eventually. But one thing that can help a lot is to take some soil from around well established nitrogen fixers and add the soil to your plants. You can sometimes dig up a part of the roots of the established nitrogen fixers to look for the nodes created by the bacteria to make sure they are present in the soil.

The area I live has native lupins that use the same bacteria as beans and native red alder that use another type. I'm planning on getting some soil from areas that have these plants growing as a way to inoculate my soil in some news beds that are in heavily disturbed areas.

The innoculates that you can buy in the store are hit and miss. Sometimes they work great but sometimes the bacteria died in the processing so you might need to add it for several years.
 
Dale Hodgins
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I scraped up just about all of the humus layer, under red alders, and used it in the garden. Most trees won't tolerate this, but it's hard to give too much abuse to a red alder.
 
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Rip up a few of the plants and cut into the root nodules and you can see for yourself what is happening with your beans right on your own soil.

If they are white they are not doing anything for nitrogen fixation, and green means they are not fixating much better. The brighter they are in the "reds"...that is going from pink to bright red, the better you can visually see how they are nitrogen fixing. I always figured pink was kicking out around 50 pounds of nitrogen per acre, where as bright red is close to 100 pounds of nitrogen per acre. My experience has been primarily with clovers and alfalfa however and not beans.

As for inoculants; I have never used them, and can get 50-100 pounds nitrogen fixation with clovers and alfalfa anyways, but we use copious amounts of sheep and dairy cow manure so I ASSUME am getting the proper bacteria from that. Inocculants cost $10 to treat 50 pounds worth of clover seed, so while I am not sure of what the recommended pounds of bean seed per acre...clover is 12 pounds to the acre for pure stands...it is not a huge cost. Cheap insurance???

One thing to keep in mind though is, depending on what your area of trees is like, it might be negatively drawing down your nitrogen. I have to contend with this when I clear forest into field. For the first several years all that woody debris breaking down robs my soil of nitrogen, so in order to get my crops to grow, I must pound the nitrogen to it and still get a lackluster crop. HOWEVER, after a few years it switches the other way and with all that woody debris now broken down, gives nitrogen back to the soil. This is why so many hugels fail. People add wood that is not rotted enough into it. All my hugels have been successful, but I have always added really rotted trees to them too.

(I realize you probably know all this Todd, and in no way talking down to you. This is more for others that may not know this information, that is all. Great topic by the way).
 
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Now this makes me wonder.  I believe I've always been told that legume crops form their beneficial relationship with bacteria to produce Nitrogen and that for some reason you need to kill/crimp/turn them before they flower to get them to release that Nitrogen.  And I've seen videos where Jerome Ostentowski will cut back a leguminous tree to pulse Nitrogen into the ground for nearby trees.  IF I remember all of that correctly, then how much Nitrogen do annual and perennial plants give off if you don't cut them or kill them?

I'm imagining a honey locust in a guild.  If I chop off a branch that is 10% of its above ground biomass, let's say it pulses 10 magic-units of Nitrogen into the ground.  Now instead, if I don't cut that branch off, does it give any Nitrogen to its neighbors?  Or does it give a little bit to be nice (1 magic-unit)?  Or still a lot (5 magic-units)?

Sorry to horn in on the thread with another question but hopefully it fits...  
 
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This is an area of much misunderstanding, so thanks Mike for bringing it up.

The legumes give off essentially zero nitrogen unless cut or killed. The reason your shrubs are so awesome is that they self-prune their roots when you cut them back, giving nitrogen in two places/soil layers. I cut my autumn olive back SEVERELY each year and the stuff around them are fantastic. I have a hugel with intermixed autumn olive/goumi and berry stuff and excepting deer pressure it is stellar.

The inoculants- Travis' suggestion is spot-on. I thought I had good inoculant levels until I dug up some plants and looked at the nodules. It was worse than white nodules, they had almost none at all! Clover will happily grow with supplied nitrogen, but won't bother setting up symbiosis unless it needs to. Think about it, it takes the plant's energy to make the sugars to feed its buddies, build nodules, etc. And I am a huge fan of inoculation on the seeds using a sticky slurry an hour or so before spreading. The people who lived here used nitrogen fertilizer and consequently the clover never bothered to make any friends.

Here is a list of the inoculants for different species, there are several that are used, and different ones sometimes in different areas. I have had poor success with certain strains of Rhyzobium and wild success with others with little regard for recommended species. I hedge everything, plant multiple species of clover (I have about 7 going right now) and use any clearance inoculant I find in my shopping. This is a good time to look for clearance inoculants in garden centers, they last only about 6 months in the package. So far the burpee inoculant for beans was best, but the hancock is fine. Just get it cheap and you can't go too wrong. I make a slurry from bean roots that look good at the end of the season and apply it somewhere else that things look wilty and not as robust. I don't do it with the clover because my seed comes inoculated and has been fabulous.

Locust apparently doesn't require inoculant or nodulate, other species like caragana and autumn olive do (apparently) but I have never inoculated, they seem to find it readily anyhow.
 
Mike Haasl
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Thanks Ty!  So I guess I need to be cutting my N fixers and not just letting them be.  If an annual N fixer dies at the end of the season, does it distribute Nitrogen then?  Or does it take it to the grave with it?
 
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Travis Johnson wrote:Rip up a few of the plants and cut into the root nodules and you can see for yourself what is happening with your beans right on your own soil.

If they are white they are not doing anything for nitrogen fixation, and green means they are not fixating much better. The brighter they are in the "reds"...that is going from pink to bright red, the better you can visually see how they are nitrogen fixing. I always figured pink was kicking out around 50 pounds of nitrogen per acre, where as bright red is close to 100 pounds of nitrogen per acre. My experience has been primarily with clovers and alfalfa however and not beans.

As for inoculants; I have never used them, and can get 50-100 pounds nitrogen fixation with clovers and alfalfa anyways, but we use copious amounts of sheep and dairy cow manure so I ASSUME am getting the proper bacteria from that. Inocculants cost $10 to treat 50 pounds worth of clover seed, so while I am not sure of what the recommended pounds of bean seed per acre...clover is 12 pounds to the acre for pure stands...it is not a huge cost. Cheap insurance???

One thing to keep in mind though is, depending on what your area of trees is like, it might be negatively drawing down your nitrogen. I have to contend with this when I clear forest into field. For the first several years all that woody debris breaking down robs my soil of nitrogen, so in order to get my crops to grow, I must pound the nitrogen to it and still get a lackluster crop. HOWEVER, after a few years it switches the other way and with all that woody debris now broken down, gives nitrogen back to the soil. This is why so many hugels fail. People add wood that is not rotted enough into it. All my hugels have been successful, but I have always added really rotted trees to them too.

(I realize you probably know all this Todd, and in no way talking down to you. This is more for others that may not know this information, that is all. Great topic by the way).



No offense taken at all Travis.  I'm enjoying everyone's inputs to the thread.  
 
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Mike Jay wrote:Thanks Ty!  So I guess I need to be cutting my N fixers and not just letting them be.  If an annual N fixer dies at the end of the season, does it distribute Nitrogen then?  Or does it take it to the grave with it?



There is no grave, only sweet rest in the soil. The nodules will release their magical elixir where they are. Bryant Redhawk covered this in another thread. It is a fine way to deposit nitrogen at deeper levels, so trees have a whack at it and the ground covers don't get to skim too much. I have been using an n-fixer right next to a consumer a la Bullock Brothers. Too early to tell but seems like a fine idea. I am propagating caragana and buy lespezeda bicolor seedlings at $0.50 for this purpose. I am also trying redbud. The autumn olive needs no encouragement! The dryest, hottest most crappy areas get lespezeda/autumn olive, the part shade get redbud or wisteria (I know but it is here already) and cooler areas get caragana. In your climate you may have to modify this system. I am also flipping it around and using honeylocust with figs right next to it or other consumers that will tolerate part shade. As the overstory tree gets bigger maybe I need to plant the nurse trees further out. I modified this to say I don't see nurse trees as a thing, they each get something, but eventually one may overtake it's buddy. This is planned succession.

Short version is I use cheap plants, take no more than a minute planting each one (just a shovel pop and stomp it in), neglect them entirely, and will see how they form their own "guilds".  The stuff that is more expensive I put tree tubes on.
 
Mike Haasl
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Thanks Ty!  So for perennial shrubs/trees I have to cut them back to get N out of them.  For annuals/biennials I can just let them die and they'll give it up at that point.  Or kill them early if I want the N a bit sooner.  Thanks for the clarification
 
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Tj Jefferson wrote:Bryant Redhawk covered this in another thread.  



You would think after reading Redhawk's excellent posts on the subject, I would understand it by now, but some of it is still sinking in.

Thanks everyone for the replies.

I'm finding that my sea berry bushes spread like wildfire here.  I may move some of the new ones around for chop-and-drop nitrogen plants.  Possibly I can prune them back enough to get the nitrogen benefits without killing them off completely, while leaving the originals to produce berries for the chickens, with enough left over for me.
 
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Todd Parr wrote:I planted a lot of beans, a hundred or so possibly, around an apple tree  and some comfrey plants where I am creating a new tree guild.  The beans are obviously suffering a nitrogen deficiency, as evidenced by their yellow color and the fact that dumping urine on them for a few days turned them to a nice dark green.  How long until beans and other annual nitrogen fixers (or perennial ones for that matter) fix enough nitrogen for their own use?



N fixers are plants that form bacterial nodules on their roots. It is the bacteria in these nodules that actually do the Nitrogen "fixing", which is a way the plant stores nitrogen for use the next year.
It will take around 2 months after planting for the nodules to begin forming if the bacteria are present in the soil, a little longer if the plant has to allow them to migrate down through being adsorbed through the stoma.
Normally the nodules will be hard at work by month 3 of the plants life span. In the case of bean plants the nodules will store N right up until the plant dies back at which point the decomposition process begins and the nitrogen will be released into the soil as the roots rot in place.

The chop and drop method came about partly to kill the plant and thus release the decomposing nodules stored nitrogen compounds before they would do so naturally.

Redhawk
 
Mike Haasl
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Oh, I came up with another question.  What about perennial herbaceous plants like lupine?  I would assume they act more like a woody perennial where you'd have to chop them to get them to give up their Nitrogen?  If that's the case, I doubt I'll be chopping and dropping my pretty lupine and then their Nitrogen fixation would not really be a help to my system.  Hopefully I'm wrong....
 
Bryant RedHawk
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hau Mike, great question.

Perennial nitrogen fixing plants such as lupine are as you surmised woody plants (for the most part).
Those nodules are not the only place in the plants that N is stored, that nitrogen is used throughout the plant, the nodules just store the excess for later use by the rest of the plant.
If you have these growing and like the look and function they perform in the landscape, you don't need to worry about chopping them down to get some benefits of their nitrogen fixation.
Plants like lupine will need some pruning so they will keep the shape you like, this will provide you with clippings which are a good source of nitrogen that you can use as a mulch or even incorporate into the soil directly.

The smaller you can cut the woody parts, the faster that stored N will become available for roots through the decomposition processes.
This is a case of "having your cake and being able to eat it too".

Redhawk
 
Mike Haasl
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Thanks Redhawk!  I like cake  In my case they are just growing in a field that will slowly transition into my food forest.  So I don't need to cut/trim/shape them since they're just out there with the grasses and other prairie plants (luckily including vetch).  If I leave them alone for the next 4 years, will they add nitrogen to the surrounding soil?  

I was planning on leaving the grassy field alone but in the past I've mowed it and harvested some of the grass for compost in the garden.  Would the sandy soil in the field improve more if I don't mow?  Or if I mow it and leave the biomass laying there?  If I mow, the lupine and vetch would get cut and release some N....

Sorry Todd if I'm hijacking your thread
 
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And another good question Mike.

Nitrogen fixing plants do not provide N to other plants until something occurs to force those plants to decay.
Proper bacteria need to be present in large enough numbers for nodules to form and then process soil born nitrogen compounds from the mineral rich soil.
This tells us that 1. we need lots of bacteria present and 2. we need enough of the right minerals in the soil for the bacteria to function correctly.
What normally happens in good working order N fixing plants is that ammonium compounds are released from decaying plant materials at the same time the stoma of the plant is inhaling free N02 from the atmosphere.
It is important to understand that free N02 is transported to the roots (where the nitrogen compound eating bacteria live) for bacterial processing, which requires the right minerals be present in the soil (they act as catalyst with the bacteria).
The same goes for the ammonium compounds in the decaying organic matter, minerals are catalytic for bacteria and allow those bacteria to break down the bonds that hold the compounds together.
Once the bacteria have broken those bonds, N becomes an ion which can be utilized by the plant.

Leaving a grassy field unto its own devices sounds like it would build soil, alas nature requires animals to enrich grassy plains, that is why the prairies started to decline with the disappearance of the bison.
Grassy plains need to be eaten, trampled and pooped on in order for the soil to become better than it was before.
Cutting the grasses to decay in place is a slower substitution for grazing animal activities, it works for us, but if we had some large bovines or sheep or goats and hogs to move through the way the bison used to do, it works faster and better.

Redhawk
 
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Todd Parr wrote:

Tj Jefferson wrote:Bryant Redhawk covered this in another thread.  



You would think after reading Redhawk's excellent posts on the subject, I would understand it by now, but some of it is still sinking in.

Thanks everyone for the replies.

I'm finding that my sea berry bushes spread like wildfire here.  I may move some of the new ones around for chop-and-drop nitrogen plants.  Possibly I can prune them back enough to get the nitrogen benefits without killing them off completely, while leaving the originals to produce berries for the chickens, with enough left over for me.



Cut those sea berries back to a stem length of @4-6 inches long and they will comeback no worries. Leave some leaf on them and definitely no worries.
let me know what portions you need help with understanding.

Redhawk
 
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Bryant RedHawk wrote:


Cut those sea berries back to a stem length of @4-6 inches long and they will comeback no worries. Leave some leaf on them and definitely no worries.
let me know what portions you need help with understanding.

Redhawk



Thank you.  It seems I'll have to plant many more nitrogen fixers than I have been if I have to chop them to get nitrogen to the soil.  I thought it worked like Mike was talking about with his "magic-units"  that get shared with neighbors.  Understand that leaf drop contributes, but for major soil inputs, it seems there will be much more chopping than I thought.  I hate the thought of cutting up my Autumn Olives, so Sea Berry it is  They spread enough that I will never have a shortage it seems.
 
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I hear you Todd, wouldn't that be a near perfect setup?

Nitrogen nodules are plant specific, however, there is a way that might work to get the bacteria to share the work to other plants and that would be micorrhizal fungi.
My new research is showing promise, it appears that bacteria and M. fungi respond to weak electrical signals sent by roots as they put forth exudates, exudates alone account for some increased activity by bacteria and fungi but it is possible the accompanying electrical pulses stimulate them even more, or perhaps that is more the trigger to stimulate and the exudates are the candy the organisms crave. I hope to know more in the coming months.

Redhawk
 
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Tj Jefferson wrote:This is an area of much misunderstanding, so thanks Mike for bringing it up.

The legumes give off essentially zero nitrogen unless cut or killed.



I'm not so sure that it's all or nothing like this. Some nitrogen fixers may indeed make nitrogen available for neighboring plants. For example, this study in Cape Cod found that black locust having established itself in the sand dune type ecology had created islands of richer soil that allowed whole communities of non-native plants to establish themselves.

Article: Nitrogen-fixing tree paves the way for other invaders

Or a pdf of the study itself.
 
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Bryant RedHawk wrote:I hear you Todd, wouldn't that be a near perfect setup?

Nitrogen nodules are plant specific, however, there is a way that might work to get the bacteria to share the work to other plants and that would be micorrhizal fungi.
My new research is showing promise, it appears that bacteria and M. fungi respond to weak electrical signals sent by roots as they put forth exudates, exudates alone account for some increased activity by bacteria and fungi but it is possible the accompanying electrical pulses stimulate them even more, or perhaps that is more the trigger to stimulate and the exudates are the candy the organisms crave. I hope to know more in the coming months.

Redhawk



That is interesting.

If that holds true I suppose it would be possible to connect the tree to a micro-jenny that put out the proper millivolts, milliamps and frequency and self-stimulate its own growth. By that I mean a tree is the idea sail and it would be nothing to secure lines to the top of the tree going back in multiple directions. As the wind blew say from the north, and the top of the tree pulled to the south, the line trailing back north would be pulled through a one way clutch and the electricity generated would be pumped to its roots. Then a spring or weight would draw the line back when the wind gust relented, only to be ready for the next gust. If the wind switched directions, that jenny would come into use. Attached in such a manner the tree self fertilizes.

An interesting concept (probably ahead of its time however) for sure!
 
Tj Jefferson
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Bryant RedHawk wrote:. I hope to know more in the coming months.

Redhawk



He has to tease us. This is a very interesting hypothesis. I wonder if the static electricity from a thunderstorm signals the plants to kick out exudates to harvest the NO2 from lightning...
 
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Quick question about lupines. I have planted a bunch in my hugel beds from seed last year and again this year and I'm considering chopping and dropping them each spring to help release nitrogen. The ones I planted last year are already about the size of a beach ball. My thought is a once a year chop could result in a fair bit of biomass and some nitrogen release.

If I cut them down each spring would they be able to regrow fully before summer? Never tried doing this with lupines.

Thanks!
 
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To answer the original question, I planted a nitrogen fixing cover crop in the third week of January.  I just terminated it this week.  11 weeks and the roots were loaded with tons of salmon-colored nitrogen nodules.  

It doesn't take long—less than 3 months.   I have to buy the inoculant because we don't naturally have the correct bacteria in the soil, so I slightly moisten my seed and inoculate it with the bacteria overnight before I plant it the next day.  Works great every time.
 
Bryant RedHawk
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Rebecca Norman wrote:

Tj Jefferson wrote:This is an area of much misunderstanding, so thanks Mike for bringing it up.

The legumes give off essentially zero nitrogen unless cut or killed.



I'm not so sure that it's all or nothing like this. Some nitrogen fixers may indeed make nitrogen available for neighboring plants. For example, this study in Cape Cod found that black locust having established itself in the sand dune type ecology had created islands of richer soil that allowed whole communities of non-native plants to establish themselves.

Article: Nitrogen-fixing tree paves the way for other invaders

Or a pdf of the study itself.



Good point Rebecca, Nitrogen fixing trees do give off excess nitrogen to the soil, their mechanism is different than the "standard N fixers" that most people thing of.
N fixing trees also give off soil conditioning exudates, and they will exhale special, water molecule attracting compounds through the stoma so there is more moist air around their crown.
When you combine all the workings of a group of N fixing trees, they are very good at creating their own microclimate, which benefits other plants and moves succession forward at a faster pace than if these trees were not there.
In the case of Black Locust, the first tree will end up creating an ever expanding colony of trees, all connected to the mother tree root system.
When this happens (and it usually does with Black Locust) the soil becomes a haven for ginseng and other medicinal plants along with the whole ecosystem associated with Locust stands.
That is one of the reasons this tree is usually considered invasive, it is a valuable understory tree that can compete with the trees of the canopy, so much so that they have the ability to kill off those trees blocking to much of their sunlight.

Redhawk
 
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I am working on a class project following nitrogen fixation and this thread has had more useful information than anything I have found to date. Thank you all for your input in the past. Hopefully this is still accessible to you all.

We are testing hypotheses, so we don't need to be right but we need to make good, testable guesses about how nitrogen and nitrogen fixers might be moving around in plants. The underlying goal is to transfer the maximum amount of nitrogen possible into our tree targets.

I have past student projects that found "pools" of fixed nitrogen (N15 depleted) around sweet clover and lupine. Currently we have a cover crop of hairy vetch and winter rye. We are still working toward the experimental design, but we want to test various ways to transfer rhizobium (and nitrogen) in a garden plot.

It's mid March and the vetch has nodules but is not activated. I have found patches of activated vetch on the school grounds. I have permission to move the soils and the vetch for experiments.

I think we are going to plant small (very small) trees in the plot so we can follow them for a year or two (the point right now is to understand nitrogen fixation, not to grow a crop). I think we have time to put down inoculated vetch. We can also move soil from the area where we have activated vetch. I can also move the wild, activated vetch.

The kicker is that we can trace the movement of N by measuring the level of depletion in N15 in plant tissues. For a couple of hundred dollars we can map the whole process with replicated experiments. We have a small budget so that is possible.

Since they are long lived we can follow the trees for over a year. New growth will contain recent sources of nitrogen.

So...where are we likely to mess this up? What hypotheses would you absolutely test? Where are you curious and what would you warn us away from?
 
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Hi Tim, welcome to permies. I am glad that you and your students are running this experiment. I don't know enough to comment on it, but I am sure someone around here will.
 
Bryant RedHawk
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Tim B Smith wrote:I am working on a class project following nitrogen fixation and this thread has had more useful information than anything I have found to date. Thank you all for your input in the past. Hopefully this is still accessible to you all.

We are testing hypotheses, so we don't need to be right but we need to make good, testable guesses about how nitrogen and nitrogen fixers might be moving around in plants. The underlying goal is to transfer the maximum amount of nitrogen possible into our tree targets.

I have past student projects that found "pools" of fixed nitrogen (N15 depleted) around sweet clover and lupine. Currently we have a cover crop of hairy vetch and winter rye. We are still working toward the experimental design, but we want to test various ways to transfer rhizobium (and nitrogen) in a garden plot.

It's mid March and the vetch has nodules but is not activated. I have found patches of activated vetch on the school grounds. I have permission to move the soils and the vetch for experiments.

I think we are going to plant small (very small) trees in the plot so we can follow them for a year or two (the point right now is to understand nitrogen fixation, not to grow a crop). I think we have time to put down inoculated vetch. We can also move soil from the area where we have activated vetch. I can also move the wild, activated vetch.

The kicker is that we can trace the movement of N by measuring the level of depletion in N15 in plant tissues. For a couple of hundred dollars we can map the whole process with replicated experiments. We have a small budget so that is possible.

Since they are long lived we can follow the trees for over a year. New growth will contain recent sources of nitrogen.

So...where are we likely to mess this up? What hypotheses would you absolutely test? Where are you curious and what would you warn us away from?



Hau Tim, what hypothesis are you currently investigating? I didn't see one listed, or did my aged eyes just not recognize it.

I've been using ammonia as a kick starter for N fixation (35 ml to 2 L H2O dilution) on some green bean plants and the nodules reacted well. Note: I always inoculate seeds with mycorrhizae prior to planting.  Currently I'm working on the interaction of tree root interaction with N fixing nodules via mycorrhizae interaction. My test plot incorporates new trees inoculated with the mycorrhizae and non inoculated bush bean plants located 1 m from the outer edge of the new trees root ball. My goal is to measure the amount of time it takes the tree mycorrhizae to reach the bean root system.  

The biggest problem (for my test) might be any mycorrhizae being present before the experiment. I created a sterile zone to prevent pre test contamination. Let me know how I can be of help.
Redhawk
 
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Hi Tim, have you already put down the script of a brief introduction? including the background of the topic, with a couple open access review papers listed, the question you are trying to find answer to, your hypothesis and the experimental design. It doesn't need to be detailed but just to clarify the thoughts.

Personally I am interested in effective ways to deliver fixed nitrogen to the target plants. Traditionally, legume cover crops are cut when in bloom and tilled in soil to decompose for a period of time before the crop is planted. With many people doing no till, the legumes are terminated and left on the soil surface instead. I am wondering how that affects the efficiency of carbon and nitrogen recycling. If they are mowed into fine fragments and withoutmaking contact with the soil, I would say the majority get oxidized quickly and turned into gaseous state. On the other hand, certain soil dwelling microbes are denitrifier, causing a significant amount of NO3- to be lost as nitrous oxides and N2.

Last year, I tested a practice to make the biomass of legume cover crops available faster for the subsequent plants.  I briefly described the method in this post.

"I grow red beans wherever space is available as cover crop. I harvest the bean leaves and dry them in the sun. Within hours they will be crispy and crumbled into powders to preserve the nutrients.  I gently loose up the soil to mix in the dry leaf powder. Compare to tilling in the bulky plant, I am able to put in more organic materials without digging a big hole and leaving air pockets. I plant seeds right away and don't have problem with fertilizer burn."

I reasoned that this should avoid the lose of nitrogen, reduce time gap for planting and minimize anaerobic condition for denitrification as the leaf powders are mixed within the top few inches of soil. I would be interested to find out how the different methods of prepping legume compared to each other in term of N15 level in the target plants during a period of time.
 
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Bryant RedHawk wrote:I've been using ammonia as a kick starter for N fixation (35 ml to 2 L H2O dilution) on some green bean plants and the nodules reacted well.



Dr RedHawk:  That's fascinating -- why do you think ammonia would kickstart N Fixation?  The general theory I've gotten from Permie/Organic people is that any soluble N will give the plant such an easy fix, that it will be less likely to invest in fixation.  I should be clear -- I'm not criticizing, I'm genuinely curious!

If you don't mind a second question...my soil is *very* sandy, and has VERY little Cobalt or Molybdenum, and I believe that's part of why N-fixers have not done well on my property.  I have struggled to find a source of Cobalt fertilizer, I do have a small amount of Molybdenum...but I am worried about it just getting washed through the sand.  Any thoughts or recommendations?  I am considering making some biochar, and including the Molybdenum in the solution I 'charge' it with -- I think it will not then wash away, but is it likely to be available to the N-fixing bacteria?

Thank you very much for the help you provide in these forums!  (I've got lots of nerdy questions I want to pester you with sometime!)

mlb
 
Bryant RedHawk
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Hau Michael, I use ammonia because it activates the bacteria that convert it into nitrogen forms that plants require. As for your soils defects mineral wise I would recommend trying to find some sea90, this produce contains over 90 minerals and can be applied around your plants. Most soils only contain 70 to 74 minerals. Sea90 is air evaporated seawater from the sea of Cortez, one of the most mineral rich waters on the planet. When applied at 1/2 cup per sq.ft. it will not salinify soils.

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