Author Topic: A reply on nitrogen fixing trees I saw on the permaculture sub on reddit  (Read 1070 times)

JoshuaTilaranCR

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Here's a link to the post

https://www.reddit.com/r/Permaculture/comments/yd3iab/perennial_nitrogen_fixers/?utm_source=share&utm_medium=android_app&utm_name=androidcss&utm_term=1&utm_content=share_button

And here's what a person, u/SaintUlvemann, replied about using them. I think it's very insightful and interesting and it cuts through a lot of beliefs that these plants are pumping nitrogen into the soil like crazy.

I'm a crop geneticist who studies legumes and knows nodulation down to many of the individual protein-protein interactions. We say that form follows function; it is typically necessary to understand what a thing is, in terms of things like shape and molecular structure, before one can understand its ecological function.

Root nodules are a novel organ that legumes (and actinorhizal relatives) develop. The organ exists in order to provide an enclosed anaerobic environment for the symbiotes to live in and for the plant to eat from. It is an internal microhabitat within the plant, that plants grow for their symbiotes.

There is a lengthy and tightly-controlled process for how plants get these symbiotes inside themselves without ending up infected with pathogens. Developing a nodule is a risky and energetically intense process; plants extract as much benefit from it as they can.

They invest large amounts of photosynthate into tasks such as feeding these symbiotes. To give another example; they regulate the oxygen content of this anaerobic environment through production of leghemoglobins. Those leghemoglobins, oxygen-binders like heme, are the reason why legume root extracts can be used to make plant-based meats taste meaty. This oxygen regulation is also energetically expensive.

Given the amount of energy plants put into developing these nodules safely, they can't just secrete nitrogenous compounds out of those roots: that would defeat their purpose. The nitrogen is produced inside of their bodies; it must be brought out of their bodies in order to make it to the environment.

The life cycle of the nodule itself provides little opportunity for nitrogen to make its way into the soil.

For those legumes with determinate nodules (meaning that the nodules are developed for a set, determinate, amount of time, and then discarded), a small amount of nitrogen may be expected to return directly to the soil at the programmatic end of the nodule's lifespan; but like the extraction of nutrients from leaves in fall, the plant avoids this waste where possible, and many legumes don't even have determinate nodules in the first place: their nodules are indeterminate in lifespan, organs that die only when the roots to which they're attached do.

Thus the route by which the nitrogen fixed by nodulating species ends up in the rest of the environment, has to be through the decomposition of the dead body parts of that nodulating plant; because the nitrogen was fixed inside the plant's body.

Mulches would be one way of doing that. The dead root systems of legumes would contain nitrogen too.

However, for many species, the majority of the nitrogen fixed by the plant is not found in the roots, leaves, and stems; it is packaged up by the plant into its seeds. Nitrogen is a core atomic building block of protein; nitrogen fixation is why beans are protein-rich. We may find that protein delicious, but from the plant's perspective, it is meant as a bequest to the next generation of the species. Annual plants' reproductive strategy is to deliberately self-sacrifice (timed to match what would be their seasonal death anyway) in order to produce higher-quality seed with the nutrients required for the developing embryo to have a higher chance of survival.

The survival strategy for perennial nitrogen fixers is not to completely kill themselves off each year; so they will reserve more nutrients for themselves. But plants that produce protein-rich seed do so for the sake of increasing the survival rate of their offspring, and perennials may adopt this strategy as surely as other plants will. This is part of why nuts and seeds are such sought-after food for animals.

The precise proportion of nitrogen that remains in the leaf, root, and seed material of a perennial nitrogen-fixing species, is likely to vary by species, depending on life strategy. I might imagine that perhaps the roots of an asexually-propagating rhizomal nitrogen fixer such as the potato bean maintained a higher nitrogen content within said roots, than a nitrogen fixer such as alder that maintains heavier seasonal investments into its reproductive structures.

Some plants that do not really fix nitrogen per se, are called nitrogen fixers due to casual associations.

The term for nitrogen fixation that is done on the outside of plants, by microorganisms that are only in casual association with them, is associative nitrogen fixation. It is harder to study, and so not as well-studied. Plants that participate in such casual relationships need not necessarily have any nodule organs; grasses lack nodules, yet have been found to participate in associative nitrogen-fixing symbioses.

Nitrogen fixed by these organisms would enter the environment via usual aqueous routes, having been fixed in the environment, not inside the body of a plant.

Jal

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Re: A reply on nitrogen fixing trees I saw on the permaculture sub on reddit
« Reply #1 on: October 26, 2022, 01:06:33 PM »
Thanks for the explanation, although I knew about the bacteria/legume association, the storage mechanism had not occurred to me. Great post

K-Rimes

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Re: A reply on nitrogen fixing trees I saw on the permaculture sub on reddit
« Reply #2 on: October 26, 2022, 01:51:11 PM »
Great post, thanks for this. Kind of confirms my thoughts that they don't actively pump nitrogen into the soil, but can be a part of a mulch in place program.

JoshuaTilaranCR

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Re: A reply on nitrogen fixing trees I saw on the permaculture sub on reddit
« Reply #3 on: October 26, 2022, 07:46:32 PM »
No problem, I found it super eye opening. I just asked if we should be collecting the seeds of the perennial nitrogen fixers and grinding them and using that along with chop and drop as the best way of getting nitrogen back into the soil from these plants. It seems that would be the way to go

Gulfgardener

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Re: A reply on nitrogen fixing trees I saw on the permaculture sub on reddit
« Reply #4 on: October 27, 2022, 08:52:56 AM »
Thank you for the write up. It makes sense! Why would any plant pump nitrogen into the soil only to have the nearest competition use it for an advantage. It's like giving away money to all of your neighbors regardless if you like them or not.

I know this is mostly for nitrogen fixing trees but I'm thinking I could crush and use almost any seed to give plants a boost. I have a ton of oaks around so I'm thinking I might gather the acorns to crush and use on my trees. They don't have as much protein/nitrogen as a legume but I have a LOT of them.

K-Rimes

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Re: A reply on nitrogen fixing trees I saw on the permaculture sub on reddit
« Reply #5 on: October 27, 2022, 01:32:30 PM »
No problem, I found it super eye opening. I just asked if we should be collecting the seeds of the perennial nitrogen fixers and grinding them and using that along with chop and drop as the best way of getting nitrogen back into the soil from these plants. It seems that would be the way to go

I just snap the stems of them when they're flowering or seeded and throw the carcass on the ground and stomp it. A bit brutal I guess but this seemed logically the best return on investment. The plant will regrow from the roots, I'm seeding, and I'm adding organic matter / N.

JoshuaTilaranCR

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Re: A reply on nitrogen fixing trees I saw on the permaculture sub on reddit
« Reply #6 on: November 01, 2022, 06:39:12 PM »
I know this is mostly for nitrogen fixing trees but I'm thinking I could crush and use almost any seed to give plants a boost. I have a ton of oaks around so I'm thinking I might gather the acorns to crush and use on my trees. They don't have as much protein/nitrogen as a legume but I have a LOT of them.

I actually asked him this exact question, if the seeds are what's pumped full of nitrogen, why not crush them and throw them around the plants you want to fertilize. I actually did that with some pigeon peas and mixed them with rock dust and tossed them around some trees.

Galatians522

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Re: A reply on nitrogen fixing trees I saw on the permaculture sub on reddit
« Reply #7 on: November 01, 2022, 09:16:00 PM »
Thank you for the write up. It makes sense! Why would any plant pump nitrogen into the soil only to have the nearest competition use it for an advantage. It's like giving away money to all of your neighbors regardless if you like them or not.

I know this is mostly for nitrogen fixing trees but I'm thinking I could crush and use almost any seed to give plants a boost. I have a ton of oaks around so I'm thinking I might gather the acorns to crush and use on my trees. They don't have as much protein/nitrogen as a legume but I have a LOT of them.

That is a really interesting thought. I ran some calculations based on your idea, and this is what I found. Proteins are roughly 16% nitrogen. If you multiply the protein content of a thing by 16% you get an aproximate nitrogen content. Based on what I found on-line acorns are about 6% protein. This makes them slightly less than 1% nitrogen. If you were growing a crop that extracted 200lbs of nitrogen from the soil per acre (an orange grove for example), you would need to apply 10 tons of acorns to replace that. Or approximately 175 lbs of acorns per orange tree.
« Last Edit: November 02, 2022, 09:37:55 PM by Galatians522 »

pagnr

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Re: A reply on nitrogen fixing trees I saw on the permaculture sub on reddit
« Reply #8 on: November 02, 2022, 05:43:47 AM »
Some years ago I investigated Veganic Gardening. Soybean meal was suggested as a Nitrogen source.
My friend who lived near a timber sawmill in Australia often collected Acacia melanoxylon Blackwood sawdust for his garden, because of the N content.
Mulching garden beds with Lucern Hay instead of grain straw hay will add additional N.
Another way perennial legumes can add N to the soil is via leaf drop and empty seedpod drop.
Acacias in Australia often have a significant dropped mulch layer underneath the trees.

Gulfgardener

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Re: A reply on nitrogen fixing trees I saw on the permaculture sub on reddit
« Reply #9 on: November 02, 2022, 02:49:31 PM »
@ Galatians522 Thank you. So not just any seed is worth the effort. It should at least be in the legume family to make a difference. Since the price of fertilizer can be crazy at times, I might be better off buying cheap dried pinto beans and crushing them every once in a while.

No true acacias near me. I'll have to see what other trees could be useful.

Jordan321

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Re: A reply on nitrogen fixing trees I saw on the permaculture sub on reddit
« Reply #10 on: November 03, 2022, 08:52:46 AM »
I was literally sitting here saying "collect and grind up seeds to use as fertilizer?! These guys are hardcore" as I sipped a cup of coffee... Think about it.

pagnr

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Re: A reply on nitrogen fixing trees I saw on the permaculture sub on reddit
« Reply #11 on: November 03, 2022, 04:54:54 PM »
Coffee grounds are about 2% Nitrogen. Some organic fertilisers blends are about that, maybe up to 3% to 5%. Animal manures would be higher again.
I find the grounds a useful liquid fertiliser, also seems to have some soil wetting ability.
Don't overdo it when top dressing pot mix with coffee grounds, it can get clumpy.
Other thing I have noticed since using the coffee grounds,
All my plants are up at the crack of dawn !