Nitrogen Fixing Trees

I was curious as to how many Nitrogen Fixing Trees that are good, that are also hardwoods for burning clean in a Wood Stove or Rocket Mass Heater.

Black Locust is what I was wanting to go with. However, the issue with Black Locust is that it attracts Bees due to the Nectar. Now, I know that Bees are very important in Nature, and that providing a good Food/Nectar for Bees is a good thing! However, I am severely allergic to Bees, so this conflicts with what I was wanting to go with originally!

Does anyone have any other suggestions for what would be a good replacement for a Nitrogen Fixing Tree?

Also, Nitrogen Fixing Trees, near a Hugelkultur Bed, is the Nitrogen able to travel up through the raised bed? How much of a radius does a Nitrogen Fixing Tree help improve Nitrogen in the Soil? How far apart is the most optimal distance for planting?

Sorry for so many questions. Still have a lot to learn!

Depends where in the world you are. Gliricidia Sepium is extremely fast growing and a very good fuel wood. But it won't tolerate cold or high rainfall.

Acacia super fast growing (at least here, where are you) and hardy. Also not a mega bee attractant if that really does worry you.

Black locust flowers mostly for a short period of time, so only would have to be away from them during that time frame. Probably wouldn't want the trees close to your home anyways, as they sucker all over and have thorns, so its a nice tree from afar.

In cold climate you could also consider alders (Alnus) which are nitrogen fixing and have wind pollenated flowers, so no bees. In tropical climates there is beefwood (Casuarina) another nitrogen fixing, wind pollenated plant.

Thank you everyone for your Replies, and Tips!

I am currently Traveling, so I don't have any land yet, but I want to get all the knowledge I need, so I know what I am doing by the time I get my own place! I plan to live down in the Southern part of the U.S. (I'm sorry, I was Born/Raised in Texas, and the Cold Weather up in the Northern States, I do not like! )

Would any of the Trees mentioned above, be able to replenish Nitrogen in a Hugelkultur / Raised Bed? Or would a Cover Crop (if I am understanding the use of a Cover Crop currently - still learning about them) do better for that, than a Nitrogen Fixing Tree?

Thank you everyone for your Help!

All trees are nitrogen fixing to some degree as well as nitrogen robbing. It really is a cycle, not a one time fix all.

In hardwoods, they drop their leaves every year, while with softwood they self prune their branches. As these fall to their base anything under 2 inches in diameter, within two feet of the ground, within two years will decay, at least in New England where I live anyway. This ultimately ROBS the soil of nitrogen as it breaks down that woody mass. After a bit of time however, about 7 years, that process changes and the nitrogen is released. In a long established forest, there is both going on every year as the forest floor replenishes itself.

That is why in a hugel you really want to add decayed woody vegetation more than new wood. You will get more release of nitrogen then it robs and therefore get better growth rates from whatever it is you are growing. However, it will have to be replenished quicker since the wood is at a higher rate of decomposition.

Cover crops are almost impossible to compare to hugel construction because they really are apple and oranges. I use cover crops on my farm, but the amount of nitrogen fixing they do is very slight compared to hugel construction simply because their lifespan is so short. I use them more for erosion control than fertilizer. It definitely is not enough to grow a high yielding crop on. With hugels (using wood) you do not have that issue, they are self-fertilized by definition since they use so much nitrogen-laden mass.

Travis Johnson wrote:
That is why in a hugel you really want to add decayed woody vegetation more than new wood. You will get more release of nitrogen then it robs and therefore get better growth rates from whatever it is you are growing. However, it will have to be replenished quicker since the wood is at a higher rate of decomposition.

Ok, now I feel foolish for asking about this, because I knew that Hugelkultur restored Nutrients as the Wood Decayed, but I completely forgot!

Trying to learn everything there is to learn, has me forgetting the simplest of things that I knew most, while trying to learn about something else!

I feel foolish now! I'm sorry guys!

Please, please, please do not feel that way. It is never my intent to make anyone fell silly. We all forget, it is just this site often runs from those with degrees in soil science to those who whom have grown up in suburbia all their lives. There is no silly questions, even concepts people have forgotten about.

They say people only retain 50% of what they are told anyway, and why I often read books again and again; picking up more and more each time.

There is nothing to feel ashamed of that is for sure; you have my respect for saying so publicly. And never forget to; for everyone that posts there are 99 that read things and never reply. A lot of times I will write a reply, not necessarily for the original poster, but for those that may come along and pick something up who may be to shy to make a post. I try to be educational to all.

Overall we are ALL just trying to do the right thing with what we are given and make the most of it.

Travis Johnson wrote:Please, please, please do not feel that way. It is never my intent to make anyone fell silly. We all forget, it is just this site often runs from those with degrees in soil science to those who whom have grown up in suburbia all their lives. There is no silly questions, even concepts people have forgotten about.

Thank you! It is a lot to learn, but I am trying!

Thank you everyone for all your Help!

Travis Johnson wrote:All trees are nitrogen fixing to some degree as well as nitrogen robbing. It really is a cycle, not a one time fix all.

In hardwoods, they drop their leaves every year, while with softwood they self prune their branches. As these fall to their base anything under 2 inches in diameter, within two feet of the ground, within two years will decay, at least in New England where I live anyway. This ultimately ROBS the soil of nitrogen as it breaks down that woody mass.

While nitrogen drawdown is a widely held belief there's very little evidence from any studies of this actually occurring. There may be some small effect right at the interface between the rotting material and the soil but that's about it both from what I've observed and what I've read in various published studies.

Travis Johnson wrote:
After a bit of time however, about 7 years, that process changes and the nitrogen is released.

Most of the nitrogen in arboreal above ground biomass is in the leaves, bark and new growth. This material rots quickly in a damp environment and the nitrogen either volatilises or is incorporated into the biota. I'm not aware of any significant long-term nitrogen recycling mechanisms from larger material. Carbon, on the other hand, definitely takes part in longer term recycling pathways particularly from larger material.

Travis Johnson wrote:
Cover crops are almost impossible to compare to hugel construction because they really are apple and oranges. I use cover crops on my farm, but the amount of nitrogen fixing they do is very slight compared to hugel construction simply because their lifespan is so short. I use them more for erosion control than fertilizer. It definitely is not enough to grow a high yielding crop on. With hugels (using wood) you do not have that issue, they are self-fertilized by definition since they use so much nitrogen-laden mass.

Legume crops are an excellent, quick way to fix substantial quantities of atmospheric nitrogen and to make this available to other plants and soil biota. Do you have any references for how hugel can do something similar? It sounds unlikely to me.

Are you talking Legume Crops or legume Cover Crops? There is a vast difference, especially here in New England. After we harvest in October, that only gives the plants a month before they go dormant due to frozen soil, then a month of growth in the Spring. There is no way a cover crop is going fix nitrogen to a very high level in that short of a time span. I know first hand they do not provide enough nitrogen to raise the next years corn crop upon, and so we must use solid cow manure to up the nitrogen, then another dose of nitrogen to form a good ear of corn. Now with the hugels we have built; that is a different story, we have had excellent results with them with no nitrogen added.

As for Legume crops (that is, NOT cover crops) that serve no other purpose than to provide feed for cows/sheep, that is another matter. We still spread liquid cow manure, but at far lower levels naturally then our corn fields. Soil tests have proven that we are at optimum levels on that, well, with the exception of lime. Again it is a New England thing; a problem with the jet stream and its topography causing serious acid rain that makes our soil VERY acidic.

That is the problems with these issues though, we must make sure we are comparing apples to apples, and oranges to oranges. Legume Crops or Legume Cover Crops?

As for nitrogen draw-down, I have cleared A LOT of forest back into field, and perhaps it is a New England only thing...I have only done so here...but it is clearly evident in the crops. Low yield and yellowing, unless you compensate with lots of nitrogen, and then you get the yield and nice green color. Its not scientific I know, but it is years and years of observation, and its good corn/grass silage in the bunker, and in the end that is what counts.

If you're defining cover crops to just mean crops used over winter then no arguments that they are unlikely to add a lot of nitrogen. Sounds like we're in agreement that legumes used as fodder crops or in a rotation add useful quantities of nitrogen.

I don't understand why you're clearing large areas of forest to make cropland as I don't see how that can be regarded as sustainable or how it fits into permaculture. If it's reforested former farmland IMO a much better use would be to use it for timber. Clearing forest for farmland is what we used to do when there were vast untapped wildernesses and we didn't care about trashing land as we could always move on to virgin land. Those days are over.

As for the nitrogen deficiency you're seeing after cutting down the trees, if it's reforested abandoned former farmland - which is common in the US NE - a useful soil test would be to check for nitrogen before you cut down the trees. From what you describe, I suspect you'll find that the soils were low nitrogen before you cleared. Agriculture generally takes a lot of nutrients out of soil. Swidden agriculture recognises this by only farming for a few years after clearing the trees. If you want high outputs consistently out of a piece of land over many years you'll generally need high inputs. And how to achieve that sustainably is perhaps the major challenge for agroecology approaches to agriculture.

Yes we are in agreement. And you are correct, no virgin timber here as it was former farmland as evidenced by the rock walls. Being a family farm for so long I have records from my ancestors that date the clearing of my last forest-into-field at around 1838, while the ring counts of the trees I am felling put their ages at around 90 years old, or put another way, abandoned as farm land at about 1926. This coincides with when tractors began to replace horses, and while the four hoofed steeds could slog through mud, steel wheeled tractors, without posi-traction and four wheel drive could not, so only the very best farmland was kept. It was also when tractors greatly improved agriculture and the crops in the US at least were worth less then they took to grow due to the higher yields. (This occurred in the 1980's as well).

Another aspect of this was the the fact that while agriculture was losing value, paper mills wee abundant here in New England because the optimum tree for making paper was via spruce and fir with its very long fibers. That changed as chemists began to experiment and find ways of producing paper with other woods. Today we can not compete with trees that grow at faster rates, do not need to be bleached, and with our expensive labor rates. Last Fall alone, in one week alone we had 3 paper mills close. Not just shutter their mills for a bit mind you, scrap them. Since I was a kid, I can think of 20 that have closed. Hemlock, cedar and fir are just three types of wood that I have in abundance that are almost impossible to market now.

One of the issues of land ownership is balance, and while I would love to have endless trees, with Maine having THE HIGHEST TAXES in the nation per capita, I simply cannot just look at trees to look at trees. With a hungry world to feed, and our annual rainfall increasing by 5 inches in the last 20 years, we have an opportunity to fill the gap by increasing agriculture production again. I am not going to put all my eggs in one basket, just as my Great Grandfather never stopped farming and turned this entire farm into forest, but on former farm ground I see no reason NOT to increase agriculture production.

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One of the reasons the scientific community is having a difficult time proving what experience to us farmers has shown is true, is because it would be impossible to draw any conclusive nitrogen level tests on forest floors due to the constant ebb and flow of the cycle. It is nearly impossible to do in fields. For example, when soil tests give us an approximate nitrogen level to apply, it is based on the assumption we are going to immediately incorporate the manure into the soil. On grass ground where tillage is not done, this is best done a day before a heavy rain, however if manure is spread, and a rain does not arrive, much of that nitrogen is lost. It is very touchy stuff. In a forest floor where it is always in flux...good luck with non conflicting results.

One of the frustrating parts of being a farmer today is that many have turned what is rather simple into something far more complex than it has to be. Back in the 1980's and 1990's it really sucked being a farmer and looked down upon by society, and while now it is nice having a little recognition for feeding a hungry world; far more farmers would be in business still if they realized not every aspect of farming is scientific equation. When I was a kid and my Grandfather and I walked across a piece of ground, he would often have me taste...yes taste...weeds. From how sweet or sour they were we could deduce what we needed for amendments, not to mention from what weeds were growing, what we had for micro-nutrients. Today the USDA requires us to do soil testing every 3 years and it is a non-needed expense. We are good on everything but lime, and that is only because we have a hard time importing it. (This is a whole other issue).

Simply put, in agriculture today we just need more farmers...

Mike Turner wrote:In cold climate you could also consider alders (Alnus) which are nitrogen fixing and have wind pollenated flowers, so no bees. In tropical climates there is beefwood (Casuarina) another nitrogen fixing, wind pollenated plant.

Just be careful planting Casuarina species that are invasive and allelopathic. For example, horsetail tree suppresses germination of seeds underneath, and can spread quickly. The tree is useful, though. Nitrogen fixing (but that doesn't matter if nothing grows around it), and very dense hardwood.

Simply put, in agriculture today we just need more farmers...

Funny I should run across this. I know it is completely off topic but I cannot resist.

I read a story today about a young woman in D.C. raising two children by herself. She could not find reliable employment, was perilously close to eviction and was out of conventional options. She was looking at living in a homeless shelter, the second time in four years, with her two kids and 18 year old cousin. 8 years ago she applied for federal housing subsidies and 8 years later she is still number 1,000 on a list of 70,000. Her tax returns offered an opportunity to catch up on her rent payments. (Story is on NPR for those interested.)

I am 22, and have been applying to farming apprenticeships throughout the New England area I live in. Most offer housing, food and sizable stipends. What seems like a dream opportunity for me, could completely change this young woman's--or other families in similar situations--life. Where I can only see benefits, "job-skill training', "affordable housing", "quality daycare services", "fresh and healthy food", and a fungible "proletariat army" to do Paul's bidding, I'm sure others offering these apprenticeships would see the challenges.

With our nation debating the necessity of expanding social programs with the challenge of not increasing national debt and agriculture facing its share of challenges I see the potential for a wonderful marriage. Between low-income families and sustainable farmers.

If you're worried this sounds a lot like Plato's republic please continue reading.
It's easy to indoctrinate the poor with tales of prosperity within arms reach (devious sense of humor, my apologies). Fortunately this sounds a lot like glorified share-cropping, 40 acres and a mule reparations (yeah, I know, I'm not funny, I'll stop).

Those farmers we need, might also be in need of their farmers. Nitrogen fixing trees seem like a good analogy to boot.

David Wood wrote:
While nitrogen drawdown is a widely held belief there's very little evidence from any studies of this actually occurring. There may be some small effect right at the interface between the rotting material and the soil but that's about it both from what I've observed and what I've read in various published studies.

Exactly, the theory is true but frankly, if it makes a difference to your soil food web, you have many other issues as well.

An elegant, 7 year, study was done near me in Auckland NZ looking at mulches which ranged from kikuyu grass left to grow through paper, polythene and wood chip.

The trees were randomly selected clones in a small space and were tested monthly for soil moisture, pH, available nutrients, including nitrogen, root development and need to renew the mulch as it decayed.
Shredded paper was best for nutrient availability but needed a lot of renewal and, because the nutrients were easily available, resulted in very little root spread.
Polythene played hell with the soil pH, dropping it sharply and contributed nothing to nutrient provision.

The best by far was the wood chip which stuck around longer, shaded soil and held moisture well and did, as expected, rob nitrogen for the first 18 months or so. After which the graph of its nutrient provision, including nitrogen, was streets ahead of anything else. The theory has legs, wood does rob N, but in the long term gives so much more back.

If you need to compensate in the short term, add some compost, rotted manure or just pee on the mulch regularly.

There are numerous Nitrogen fixing trees/Shrubs.

Goumi - https://en.wikipedia.org/wiki/Elaeagnus_multiflora
Siberian Tree shrub - https://en.wikipedia.org/wiki/Caragana_arborescens
Red Bud - https://en.wikipedia.org/wiki/Cercis_canadensis
Alder - https://en.wikipedia.org/wiki/Alder
Russian Olive - https://en.wikipedia.org/wiki/Elaeagnus_angustifolia
NewJersy Tea - https://en.wikipedia.org/wiki/Ceanothus_americanus

Perennial Tubers/Vines

Groundnut - https://en.wikipedia.org/wiki/Apios_americana
Wisteria - https://en.wikipedia.org/wiki/Wisteria_frutescens

Here is a fairly complete list - http://www.perennialsolutions.org/all-nitrogen-fixers-are-not-created-equal

Enjoy...

For mild temperate and subtropical places, you could use tagasaste (Cytisus proliferus). It's drought tolerant, frost hardy to -9C (seedlings can be killed by -2 though) and about the only thing it seems to be intolerant of in my experience is waterlogged soil. The wood is dense and burns well. The foliage makes good fodder and the flowers, which appear in late winter here in NZ, are a major food source for nectar-feeding birds and early bees.

Some acacias are useful, but check to see how invasive they are before you go planting screeds of them. If you're somewhere that gets hot, mesquites are amazing.

Phil Stevens wrote:For mild temperate and subtropical places, you could use tagasaste (Cytisus proliferus).

My experience too. Great little trees, quite short lived apparently, mine are still only a few years old, great flowering plants in late August where I am but really touchy about waterlogging; mine have grown really fast and died already in a couple of wet patches, the rest are going great.

I celebrate every time an Acacia is cut down. They say it's NOT allergenic but I spend any time around them sneezing profusely. Several of the plants listed are invasive and spread quickly. So read up BEFORE you plant. Why send your time grubbing out trees or living with an allergic problem?

Fukuoka planted crops according to what weeds grow in an area.

Nitrogen trees are most beneficial when you coppice them to cause a die back or self prune of the roots and their nitrogen nodules. Their leave provide a nitrogen boost also. I like the mimosa family of trees including lecueana. They all make pretty good fire wood.

Observed a pod producing tree by the skatepark (and all over the area, norcal coastal Humboldt ) acacia dealbata but i have to run.

As i was saying. Acacia dealbata aka silver wattle is around here, fixing nitrogen, and doing its thing. I picked up some seeds poured boiling water on them and soaked overnight. Stuck them in a pot and forgot about them for a month and voila ive got baby acacias.ok i did keep the pot moist. So just wanted to share that. Is anyone else growing this tree? I hope its not allelopathic