Legumes not fixing nitrogen

I've always found nice pink nodules on garden legumes, though I've never inoculated.
I'm helping develop a young orchard into a community food forest,
and before I got into the complexities of inoculating for exotic species, I thought I'd check the garden plants that are already there for nodulation.
I have just dug up: fava beans, lupins and clover to check for nodulation.
No pinkness that shows nitrogen fixation. At all. On anything on the site.
I have a scared feeling I need to source specific rhizobia for lots of things, although I found a useful pdf (attached) that shows some cross-species nitrogen fixing bacteria.
It's basically pasture plants; who knows what I do about trees!
Does anyone else get the impression there's lots of 'thou shalt plant nitrogen fixers', but little explanation of what that actually means/requires?
I suspect there's lots of people (myself included) merrily growing legumes and assuming they're fixing nitrogen,
but unless the correct bacteria are already there, there is basically no nitrogen being fixed.

Sometimes, I do get the impression that there is "thou shall plant nitrogen fixers" going on because it might be assumed that everyone paid attention during basic biology in grade school; I remember learning the cycles of nitrogen, phosphorus, carbon, and water then. Anyhow, there is a nice half-hour video from YouTube explaining the nitrogen cycle:

New Mexico State University has a guide discussing nitrogen fixation, and they go beyond saying what color the nodules should look (like how you described, pink or red) and state that if the nodes look green, grey, or white nitrogen fixation has stopped. They also describe how expensive it is for plants to feed nitrogen fixers.
I would like to parallel this discussion with Toby Hemenway's thoughts about nitrogen fixation because in Gaia's Garden he mentioned that plants go through natural rhythmic cycles of growth, decay, dormancy, and regrowth which are in tune with the seasons and weather changes. This makes me think that, when combined with the concept of nitrogen fixation being an expensive process, that the plants may have been caught in a dormancy period when you checked them. This, in turn, could mean that the plants will and are fixing nitrogen during regrowth and growth cycles in their life. going back to Hemenway, nitrogen fixation could also be affected by the local weather and climatic cycles, too.

OK, back to the issue of if they (the bacteria) are there:

I do not think you should be too afraid because there are free-standing nitrogen fixers out there that do not require a symbiotic relationship with plants, and they can contribute a large amount of nitrogen into the soil. Check out the document I've attached to this post; it goes into a little more detail about the free-standing microorganisms. The most important thing they mentioned- again- is that nitrogen fixers are hungry little buggers! For a very detailed explanation, there is a research paper online that discusses azotobacter and how wide spread it is, and the results are more surprising than you would think.

Here are some other neat things online:

USDA talks about cover crops:


Paul Brown gave a talk about healthy soil:


Another discussion on soil ecology:


I would not be surprised if some of the fungi and bacteria

There is another nice website with information on perennial and native nitrogen fixers. Some plants like, kudzu, were surprising to learn were great nitrogen fixers.

Finally, some places to buy inoculation include GrowOrganic, Bountiful Gardens, John and Bob's, and Paul Stamet's Fungi. The last two, I am unsure whether they contain nitrogen fixing bacteria or not.

A lot of the extra information was added in the EDIT so that anyone who posts has quick access to information which can establish common ground and fast forward the discussion a bit.

Thank you for your detailed post and links Dave

Dave Burton wrote: it might be assumed that everyone paid attention during basic biology in grade school

All I remember learning is the basic 'legumes-nodules-bactera-nitrogen fixation' kind of thing, but it was many moons ago
I just didn't realise the complexity of it all till now-mainly because I just didn't think about it...

Like all of the commonly used permie nitrogen fixers in NZ are exotic,
and none share nitrogen fixing bacteria with our native species.
So unless the area was previously inoculated with the right bacteria, it has to be brought in.

NZ has extremely strict border biosecurity, and they would most probably confiscate any bacteria I tried to import.
I will probably be able to find inoculants for most legumes, but I may need to rethink getting seed for a couple of unusual species.

Anyone else out there playing matchmaker with bacteria and plants?
I feel vaguely like I'm missing something-what do you do when you plant a species where the right rhizobia isn't going to be there?

If you have been growing the same species in that area for a while, I'm sure the bacteria and others will have found their way in. If ordering innoculants from abroad is not an option, maybe one of these two ideas could be possible? 1) Poke around online and see if anyone is selling inoculant in NZ. or 2) Look around your neighbourhood and see if the same types of plants are growing in your area, and then ask the owner if you can dig up a cupful of soil from near the plant to take home and use as an inoculant...?

Why do you think "none share with your native species"? Have you tried talking with any of your local universities or college research extensions?

I wonder if it could be that the soil in the area in question is already high in nitrogen from whatever source. I believe this can inhibit nodulation and fixation.

Alder Burns wrote:I wonder if it could be that the soil in the area in question is already high in nitrogen from whatever source. I believe this can inhibit nodulation and fixation.

Good thinking Alder! I found a guide online to identifying plant nutrient deficiencies along with a visual:



By looking at the deficiencies or lack thereof, one could determine what is going on in their soil. This could also be used as an indirect method of observing the nutrient composition of one's soil. Once again, one could call their local universities to see if they will analyze a soil sample for you.

Leila, David and Alder are making good points about the availablity of nitrogen. Do you actually see any physical evidence of nitrogen deficiency? If not, why are you devoting so much attention to it? I to have been taken in the mantra of "plant nitrogen fixers", but my personal experience so far has been ho-hum. That is, the fixers I've planted seem no more thrifty than any of the other non-fixing trees. Not saying is isn't important, though what I am saying is that on my own peice of land, I have not seen any actual benefit from fixation in my real trees in the ground.

Again, another example of "they say" rather than "I've seen".

Rebecca Norman wrote:Poke around online and see if anyone is selling inoculant in NZ

We do a good line in dairy in NZ-I can buy inoculated clover, alfalfa etc but trees...not so much

Rebecca Norman wrote: Look around your neighbourhood and see if the same types of plants are growing in your area, and then ask the owner if you can dig up a cupful of soil from near the plant to take home and use as an inoculant...?

I've got my eye on a friend's healthy-looking Tagasaste

Dave Burton wrote:Why do you think "none share with your native species"?

here's one article. It's actually not as unequivocal as other I've read, but of course I can't find them now

Dave Burton wrote:Have you tried talking with any of your local universities or college research extensions?

I've exchanged emails with a rhizobia guy; I will probably hassle him some more...
We don't have an 'extension' system like the USA, but I might contact other people that know stuff as it's pretty fascinating to me!

Alder Burns wrote: it could be that the soil in the area in question is already high in nitrogen

I guess it could, although I'd be pretty surprised.
The area has had a couple of years of heavy feeders, and no amendments.
Maybe I underestimate clay soil's abilities, after spending most of my time playing in sandpits

Michael Qulek wrote: Do you actually see any physical evidence of nitrogen deficiency?

No I don't, but I've always been taught that a sustainable food forest needed efficient nutrient cycling
and a sustainable way to provide nitrogen in the long-term was to plant nitrogen fixers?

Michael Qulek wrote: If not, why are you devoting so much attention to it?

fear not, it's not exactly consuming me!
I'm just curious, and interested in others' thoughts/experiences.

Nitrogen fixers need other micro-nutrients in order to fix nitrogen. Calcium (Ca) is a major factor. See the following:

http://www.bepls.com/march2013/14.pdf

Karen Walk wrote:Nitrogen fixers need other micro-nutrients in order to fix nitrogen. Calcium (Ca) is a major factor

I wouldn't be at all surprised if this was an issue-apparently NZ soils tend to be really low in calcium.
I'm getting a lab soil test in spring
Rather exciting in a nerdy kind of way!

It might not just be bacteria, but most woody plants have fungal associates that improve fitness. I had an acquaintance with a grower who when gathering seeds would pull up a root and strip the rhizosphere soil into the seed bag with the seed, bringing it back to the nursery to inoculate the future potted stock.

Lelia,

In your situation what you could do to introduce the appropriate bacteria is to find a plant (i.e. the Fava beans in your example) that is fixing nitrogen, uproot it, crush the root system and nodules into a bucket with a little bit of water. Use the resulting slurry to soak your seeds in before planting - then water in the seeds with the left over water in the bucket. That's one way of introducing the bacteria to a new sit - but it relies on you having that initial plant that already has a good association.

I've taken a slightly different approach, in that I've been (attempting) to use our native NZ nitrogen fixers as much as possible at my place (I'm in the BoP), however it is hard to get them started due to pest pressures. But by going with the NZ native species it's easier to get the right associations underway as they're already present in our soil. Plus in some cases it's helping some native species that are threatened in the wild. But I would say that overall they're not as all round useful (i.e. they're not edible) as the imports!

Apologies if you know this but below I'll brain dump what I found out about our native Nitrogen fixers etc. These are just my own notes collated from all sorts of places - so treat them as the uninformed gossip they probably are!

I split the Nitrogen fixers here in NZ into two groups (legumes and "other") :
There are four genera of native legumes here:
1. Sophora (Kowhai)
2. Carmichaelia (New Zealand Broom)
3. Clianthus (Kakabeak)
4. Montigena (Scree pea)

There's some interesting research in NZ about our native legumes and their associations, I learnt a lot from this thesis:
http://www.rhizobia.co.nz/downloads/Weir2006_PhD_thesis.pdf

Including this gem:
"This study indicates that most rhizobia isolated from New Zealand native legumes are members of Mesorhizobium, and all isolates obtained from the introduced legumes studied are members of Bradyrhizobium."

The three other native non legumes Nitrogen fixing species:
1. Tainui (Pomaderris apetala) - Actinorhizal association
2. Golden Tainui (Pomaderris hamiltonii) - Actinorhizal association
3. Matagouri / Wild Irishman- (Discaria toumatou) - unknown association.

I couldn't get a hold of Scree pea or Matagouri, but have tried the others.

In the end, I've been trying to use Kakabeak as my main nitrogen fixer, mainly because it's endangered in the wild and looks nice however I'm having a lot of trouble getting it established due to rabbits and slug/snail damage. It's not really vigorous enough to become the sort of "chop and drop" crop I'm ideally wanting. I've also put in some of the Giant flowered broom (Carmichaelia williamsii) too - which does a bit better against predators but isn't what one could call "lush"! I had some Golden Tainui too (it's also known as "Gum-diggers soap" as the flower heads produce a soapy lather!) but that died off - I must get some more in! . I've been establishing Kakabeak from seed as the seed is widely available and much much cheaper than buying plants.

Anyway, a bit of a long rant - but don't ignore NZ's own native nitrogen fixers - they may not have the all the benefits of the imports (notably edibility) but they're well worth a look at on their own.

Thanks for you post Alex-lots of good info and it's always lovely to hear from 'local' people

Alex Slater wrote:by going with the NZ native species it's easier to get the right associations underway as they're already present in our soil

I'm very much with you on this and I've been mulling it over for a while.
Actually, my 'thing' in a food forest isn't edibility as much as growth:
in my experience, most NZ legumes take their time growing, and many don't appreciate the heavy pruning associated with 'chop and drop'
But kakabeak loves a good haircut... it's a fickle plant for me though
have you found a native that works well in a food forest?
I'm definitely not anti-native, it's just that they don't seem to be as robust as Siberian pea shrub, tagastaste etc
I'm not worried about tagastaste-I can get soil from good plants

Leila Rich wrote:<snip>
in my experience, most NZ legumes take their time growing, and many don't appreciate the heavy pruning associated with 'chop and drop'

I totally agree (sadly!), they just don't have that rampant growth that would be ideal.

Leila Rich wrote:
But kakabeak loves a good haircut... it's a fickle plant for me though have you found a native that works well in a food forest?

I have quite a few Kakabeaks, but they get eaten down to sticks by rabbits etc (but I keep on plugging away). So I guess the answer is "no" as I haven't found a NZ N-fixer that works well. That said, I guess perhaps we should look outside of the usual and investigate other NZ pioneer plants (though they don't fix any N), Manuaka would be a good choice (bee attractant + vigorous) as a chop and drop, or how about Wineberry (Makomako)? I've got these in my hedgerow (along with NZ's native giant tree fuchsia as it has edible berries and looks great). I'm also a fan of the NZ tree daisies (Olearia species) as they look great and have a lot of bee fodder, plus the ever popular and varied hebes.

Following up on Alex's comment about other useful native plants, I have had good success with coprosma robusta as a fast growing hardy evergreen. Seems to stand up to the dry and has small berries that birds and chickens will eat. Comes up from seed very readily.

When it comes to chop and drop, nothing beats tagasaste for my climate. I have also been using fennel as a soil builder as it creates a substantial root network even in clay in a season or 2. Can be hacked back periodically and colonises and area well. Insects love those umbelliferous flowers and these in turn feed wax eyes.

Tutu (Coriaria spp) is also a non-legume nitrogen fixer (and pest resistant)

http://researcharchive.lincoln.ac.nz/dspace/bitstream/10182/2710/1/ipps_v51_pp94_97.pdf

http://newzealandecology.org/nzje/2672

I should be pointed out that for Tutu "Most of the plant parts are poisonous, containing the neurotoxin tutin and its derivative hyenanchin".
Surprisingly, even honey collected (indirectly) from the plant can be poisonous.

Probably not the best addition to a food forest.

True, esp for public food forests (for private gardens, I think it's good to teach people to not eat things unless they know what they are).

I've heard of the honey poisonings, but don't know what bee keepers do given it's a fairly common plant in places.

I also quite "scrach my head" with this sort of question!
Actually, I have looked at legume roots, and NEVER saw anything that would look like I have read about "nodules". nothing on roots, and they are said to be visible???

I have local legumes like tagasaste, also tedera and some vicia etc, but what about the pigeon peas I sow from seed?? What about my garbanzos and fava?

About buying inoculators: never saw any for sale, and do not think they can travel by plane and stand the large range of temps they will have to experience....