Lack of nitrogen fixing nodules.

I have tried many nitrogen fixing plants, and I have yet to ever witness an actual nodule on the root.  Has anyone experienced this?  I have tried crimson clover (the was inoculated,) hairy vetch, rattlebox (crotalaria)  this is growing wild, various beans, peas, what's the deal?  Anyone experience this?  It is very sandy soil but I often amend with local organic matter.

Yes, I've experienced it.

I always buy the bacterial inoculant with my seed purchase and I always inoculate according to the directions.  3 years out of 4 it works.  But occasionally, I seem to get poor inoculation and poor nodulation.

People say that once you've inoculated nitrogen fixing seeds, the bacteria will forever be in your soil and you'll never need to purchase the inoculant again.  I've not found this to be true.  Every year I sew a small test patch in an area that had been planted with n-fixing cover crop seeds the previous year.  If I get any sort of nodulation, it's minimal.

My hunch is that you need to more carefully inoculate your seeds before planting.

Thank you that is very helpful...I have a strong suspicion the soil has something to do with this.  It is very sandy and drains heavily, I wonder if the bacteria is quickly washed out of the soil.  I will experiment with this, thanks!

I've always heard that n-fixing inoculates have to be kept from getting too hot before application. A morning in a hot truck cab will kill them.

Interesting about the heat... I planted the crimson clover which had that inoculation coating and I threw it right on the surface.  Even in cool season it gets hot out in the open sun, I wonder if it could have been too harsh?

I hope Dr. Readhawk comments on this but I think both points are valid, the bacteria need the humus environment and are sensitive to heat and ultraviolet. I also wonder if soaking the seeds so the root starts to form before inoculation would be more effective. Keeping roots in the soil constantly that feed the bacteria would be ideal. Keeping a blanket on it to protect it is next.
Dirt needs cultivating, soil does not. Disturb the soil only enough to remove unwanted plants and transplant or plant wanted ones.

hau Chris, I hope I can shed some light on this subject for you.

First off let's talk about those "inoculated" seeds on the market. Most of these "N fixer" plants are available with a two part coating which is designed to 1. prevent damping off for good seed germination and 2. a thin coating of bacterial inoculant when advertised to have it.
There is a problem with how those seed inoculants are used. What happens is that the seed goes through the first coating which is always the damping off coating, then they add that thin layer of bacteria inoculant, the problem is, these are put on backwards.
Bacterial inoculants and fungal inoculants both need to be touching the seed coat, sadly that never happens unless you are adding the inoculant yourself, all companies are using the assembly line to get every seed in the run properly coated with the damping off materials first, that is their primary concern.
The fungi/bacteria seem to be a stab at being able to market that their seeds have a growth inducing seed coat, but since that seed coating isn't directly touching the actual seed coat, when the root first begins to expose itself, there isn't anything but a damping off concoction for it to come in contact with.
This isn't a bad thing at all, but it does mean that the bacteria/fungi layer has already dissolved and sadly there are damping off seed coatings that actually kill bacteria and fungi as they are trying to establish.

Mycorrhizae are generally not used in either of these seed coatings (which were designed for commercial operations) which means we still need to mix these products with water and a little complex sugar and water in the seeds with this so our new root systems actually have the things they need to thrive, available.


I use many seeds in our pastures that are coated seeds but I still come back once the seeds have sprouted and once they have their first set of true leaves I water them with a mycorrhizae solution.
I wait that two weeks so that any of the damping off compound(s) have had time to dissolve, do their work and start breaking down, no sense in spreading mycorrhizae when there are killer compounds active in the soil around the new seedlings.
This also works for grasses including bamboo.

Now about nodules forming on nitrogen fixing plants, even if you do have soil full of the right bacterial forms, you need to have plants with a need for extra nitrogen so that the roots form the nodules for the bacteria to live in, fix N and store it.
If your soil has ample N content, don't expect to find nodules, they aren't needed in this particular type of case.
N fixing bacteria generally fix Nitrogen that comes from the air the plants and bacteria breathe, so if the soil has ample N, the bacteria have no need to pull N from the air and store it.
What this means to us, the gardeners and farmers, is that when we plant N fixers and don't see any nodules form as the plants age, the bacteria are telling us that our soil mineral/nutrient levels are good, at least for now.

Hope that helps

Redhawk

I plant my cover crop in mid-October.  The seed mix include several types of nitrogen fixing legumes (various beans and peas, lentils), clover, oats, vetches (of several varieties) buckwheat, and a few others.

Two days before I'm going to sew the seeds, I'll dump them into a 5-gal pail and mix them with about 2 gal. of fresh rainwater or other non-chlorinated water (don't use tap-water, as the chorine will kill the bacteria in the inoculant—even 2 days later).  Seed swells once it gets wet, so you can't fill your bucket all the way to the top with dry seed.  Maybe fill it 2/3rds of the way full before adding water.

By the next day, all that water has been absorbed by the seed.  I'll turn the seed by hand, or dump it from one bucket to another, just to make sure everything has been evenly moistened.  

I'll add the inoculant to the bucket of moistened seeds the night before I'm going to sew the seeds.  It's black and powdery, like black flour.  I'll mix it well with the seeds and let it sit overnight.

The next day, I'll sew the seeds.  Normally, I'll rake-back the wood chip mulch that covers the garden and orchard, broadcast the seeds over the bare soil, and then throw the mulch back over the seeds.  This is enough soil to seed contact to assure effective germination, and it keeps the inoculated seeds from being irradiated by the UV rays of the sun.  Germination is evident within a couple of days and within 2 weeks, there is a 3 inch carpet of green throughout the garden/orchard.

A month and a half later (today), the cover crop is about 12 to 18 inches high.  No sunlight is reaching the soil anymore—it's a giant biological solar cell, capturing energy and transferring it to the soil below.  The legumes are showing nitrogen nodulation.  My chickens have been turned loose into the cover crop (from which they were excluded for the first month) and they gobble up the tender young oat plants and peck at some of the other leaves.  

I'll let it grow till the second week in January, when I'll have a class of students over to the house to pull it up and build a massive compost pile.  Where cover crops are growing in the raised beds, we'll use a hedge trimmer to clip them back to the surface of the soil (no till) and leave the roots in place.  Otherwise, everything else gets pulled up and piled up.  Some of the nitrogen nodules are left in the soil when you yank the plants out, but much of that N goes into the compost.  I'm very conscious of the green to brown ratio of this compost pile, as I don't want all that N to gas-off.  I'll make sure that there is plenty of dry straw and shredded paper in that hot pile.  It doesn't make sense to go to all the time and expense of raising a nitrogen fixing cover crop if you're just going to yank it out of the ground and let it gas-off in a hot compost pile.  I wish I could graze the cover crop down with cows, but alas, I live in the suburbs 15 minutes from Disneyland -- not exactly America's agricultural heartland.  

How much of the bacterial inoculant remains in the soil from year to year?  I don't risk it and assume that the correct bacteria will be there.  I re-inoculate every year.

Best of luck with your experiments.

Sometimes you still get nitrogen fixation without seeing much for nodules on the roots.

What does the soil report say for available nitrogen before you plant, versus after you plant?

Travis Johnson wrote:

What does the soil report say for available nitrogen before you plant, versus after you plant?

We had our soil tested (I think university of florida) and they claim they do not test nitrogen because it fluctuates too much.  Is that true and "normal"?  Suspicious...
Anyway it wasn't part of the report.  However most nutrients were rock bottom (minus phosphorous, off the chart, because, well, Florida I guess).  Its quite barren in its natural state.  By the way this has been some fantastic information.

So one sees a lot of nodules if N levels are low? I have planted a lot in forest soils largely populated by red alder (Alnus rubra) and noted that alder growing in sandy soils produces a lot more nodules.

I have also seen nodules form in rotting alder sawdust; seaberries (Hippophae rhamnoides) in sawdust trench storage still form nodules. Interesting that Frankia bacteria would be working in an environment so unlike soil!

Does the size of the nodule indicate anything? I have seen some the size of a kumquat.

hau Fredy, since you have asked;

Frankia is a genus of nitrogen-fixing, bacteria that live in symbiosis with actinorhizal plants, similar to the Rhizobium bacteria found in the root nodules of legumes in the family Fabaceae. Frankia also initiate the forming of root nodules.

Frankia is of fundamental and ecological interests for several reasons including its wide distribution, its ability to fix nitrogen, differentiate into sporangium and vesicles (specialized cell for nitrogen-fixation), and to nodulate plants from about 24 genera.
" Species of the Frankia Genus are Gram positive bacteria.”

At least 80% of all angiosperms are able to participate in AM symbiosis while only ten families of angiosperms are known to form symbiotic association with nitrogen-fixing bacteria in root nodules.
In addition to occurring with rhizobia in the legumes and Ulmaceae, nitrogen-fixing symbioses involving root nodules also occur with Frankia in some members of Betulaceae, Casuarinaceae, Coriariaceae, Datiscaceae, Elaeagnaceae, Myricaceae, Rhamnaceae, Rosaceae.

In legumes and nonlegumes alike, the actual fixation of nitrogen is done by bacteria living inside the roots of the host plant.
It is a classic example of a mutually beneficial symbiosis: the plant provides the bacteria with sugars and a variety of minerals, and the bacteria provide the host with a usable supply of nitrogen.
In the case of the legumes, the bacterium may be one of several different species of the genus Rhizobium, a rod-shaped bacterium found naturally in most soils and available commercially in most seed catalogs as legume inoculant.
In the nonlegumes, the bacterium involved is an actinomycete, or filamentous bacterium, in the genus Frankia.

Unlike the rhizobia, which exist as discrete cells, the actinomycetes grow in long chains of cells similar to fungal hyphae, but much smaller.
All of the plants infected by Frankia, with one exception, are trees and shrubs, whereas among the legumes both annual herbs and trees may be infected by rhizobia.
The microorganisms enter the plant through the root hairs and grow in the cells of the roots, stimulating them to grow and divide.
Both Rhizobium and Frankia bacteria possess special enzymes, nitrogenases, that allow them to transform the nitrogen gas in the air into ammonium which, in turn, is converted into amino acids.
Because the reaction can only occur in a low oxygen environment, the process is often dependent on hemoglobin compounds found in the nodules, which are virtually identical to those found in the red blood cells of animals.
By binding with oxygen, the hemoglobin in the nodule helps to create the microenvironment that the nitrogenase enzyme requires.
It is interesting to note that when actinorhizal plants are grown in water culture, the young, succulent nodules are often pink in color, due to the presence of hemoglobin.

It is primarily because the legumes are involved with food production that they have attracted the lion’s share of scientific attention, but this situation is changing rapidly.
People are becoming aware that the potential value of actinorhizal plants is of equal importance, if not equal conspicuousness, to the legumes.
Experiments have been conducted by forestry managers in which actinorhizal plants are grown in conjunction with various economically desirable trees:
red alder and Ceanothus with Douglas fir on the West Coast, alder with poplar for pulp on the East Coast, and Elaeagnus with black walnut in the Midwest.
In all cases, the experiments resulted in richer soil and faster growth rates in the desired tree species.
In the Northeast, sweet fern, bayberry, and Elaeagnus are used extensively for stabilizing roadside bankings and revegetating traumatically disturbed ground.

Nodule size can be an indicator of which type of nitrogen fixing bacteria are present. (smaller normally means Rhizobium, large normally means actinomycete).

Redhawk

Chris Mike wrote:

Travis Johnson wrote:

What does the soil report say for available nitrogen before you plant, versus after you plant?

We had our soil tested (I think university of florida) and they claim they do not test nitrogen because it fluctuates too much.  Is that true and "normal"?  Suspicious...
Anyway it wasn't part of the report.  However most nutrients were rock bottom (minus phosphorous, off the chart, because, well, Florida I guess).  Its quite barren in its natural state.  By the way this has been some fantastic information.

There is an extra charge for available nitrogen.

Nitrogen indeed is fickle, but it is better to test for it and get an idea than not.

But you do not need a soil test to check the plants for available nitrogen if you do not need exact measure, like what to put on the field for NPK. You can always look on individual blades in the sward, and see if there is an inverted Vee on the plant. If there is, that is a sure sign you are NOT getting nitrogen fixation. You generally can see it across a field, a pea green color to the sward instead of a dark green color means it is craving nitrogen. If you see a purplish color, you need phosphorous.

You can also taste the sward to see if it needs the PH moved. If it is sour tasting, you need to sweeten it up with lime. If it is overly sweet, you need to use a bit of sulfur to knock it down. Again you will not be using this to get exact amounts of lime or sulfur, but it can give you an idea of what is going on for NPK/PH in the soil.

Whoa Dr Redhawk, this was a lot of typing! I hope it wasn't covered in your soil series, which I am slowly working through when I don't have enough else to read here (rarely). You answered a lot of questions I haven't even formulated yet.

All of the plants infected by Frankia, with one exception, are trees and shrubs, whereas among the legumes both annual herbs and trees may be infected by rhizobia.

What is that one exception? I have very little experience with Rhizobium, but a fair bit with Frankia, and I can't turn soil at my place without finding nodules. It's become a party trick for explaining nutrient cycling to visitors. But I wonder if I should encourage Rhizobium as well, come next spring. There are probably some on the many patches of wild & some cultivated clover that I have around.

This also makes me wonder about my soil pH, which I have never comprehensively tested. In "Teaming with Microbes" the authors assert that "nitrogen fixing bacteria generally require a pH above 7." But then "As soils become dominated by fungi, the populations of n-fixing bacteria required to convert ammonium into nitrates diminish because the pH is lowered by the acids the fungi produce." My soils seem to be both very fungal (just from looking at leaf litter and how quickly it myceliates, or how thoroughly flushes of, say, Sulfur Shelf or Dead Man's Fingers or Angel Wings dominate) and neutral/base. Due to historic logging, there are not a lot of conifers around to lower pH. Fungal prevalence vs. N-fixing bacteria sounds either/or and I'm sure it's more complex than that.

I also think there is an aerobic component to this process, that is, if oxygen availability drops below a certain point, it stops. But I can't find where I noted this in the books.

Because the reaction can only occur in a low oxygen environment, the process is often dependent on hemoglobin compounds found in the nodules, which are virtually identical to those found in the red blood cells of animals.

The plants provide the hemoglobin as well as the nodules?

Nodule size can be an indicator of which type of nitrogen fixing bacteria are present. (smaller normally means Rhizobium, large normally means actinomycete).

Having never seen a Rhizobium nodule, I had to Google them...I guess by "small" you mean "from the size of a brassica seed to a currant".

This is probably a good place to ask another question that's been bugging me: what is the best use for severed nodules? I've been burying them whole with whatever I'm planting. Maybe I should be chopping them in pieces, or putting them in a solution for dispersal, or both?  Can Frankia populations be cultured a la compost tea? Would there even be any point to that in soil amply shot through with noduled roots? I don't know what happens to Frankia populations in a nodule when they are severed from a network.

"Teaming with Microbes" also says "some studies suggest that Frankia species can fix nitrogen without the association with a plant root," what?? Unfortunately they eschewed footnotes/endnotes.

ok Fredy, Actually there are two plants that use Frankia instead of Rhizobium bacteria for N fixation, the first is sweet fern and the other is sweet grass found in the great plains.

The main thing to remember about actinomycetes is that they are much slower growing than Rhizobium species. This means it takes them longer to populate a plant, once they establish though, you can tell because the plant will start growing very rapidly.

If you grow peas, beans and other legumes, you have Rhizobium not actinomycete bacteria working in the roots.

There seems to be some confusion about the role of pH in N fixing bacteria mostly from where the scientist writing the report lived and worked (this needs a regional report built) different parts of the planet use different strains of both types of bacteria.
Fungi work in sync with the N fixing bacteria in most cases. The problem is that where you find lots of fungi hyphae the soil generally has enough N available which means the bacteria are going to go else where since there isn't any need for them in that location.

Low O2 does not equate to No O2, anaerobic conditions will either kill or shut down bacteria that want even one molecule of O2 for respiration needs.

Yes the plants do have hemoglobin compounds as do the bacteria

Rhizobium nodules can be the size of a full grown butter bean, Actinomycete nodules can be the size of a Soft Ball. (hence my reference to "small" nodules with Rhizobium)

Severed nodules are best used as "seed" you slice them in half and then place them next to a living root. Optionally, you can do as you have described doing, both work, the sliced nodule will just give up the bacteria faster.

Teaming with Microbes has (in my opinion) some erroneous information which was caused by the timing of the book being written more than an author error possibility. (most of what I offer up on this site is current (last year or this year research done by me and my assistants)
Once a book is written, any new information from research means a new edition of the book has to be written. (my book will offer (at least I hope this will be the way it goes) yearly updates so the purchaser of my book has the opportunity to stay as up to date as possible.

Redhawk