Nitrogen fixation bacteria

Nitrogen fixation bacteria in the roots of legumes provide the element for our amino-acids; they are an essential part of the fundamentals of choice foods.

These little bugs may make for a rather dull subject at first sight, but it is actually vitally important for every serious gardener to appreciate, even if not totally understand. And, if you have any sort of science or biology background, you will find it fascinating; at least, I did. 

Why are these bacteria so important? Because a shortage of the element nitrogen is the biggest limiting-factor in your vegetable gardening.

Low-nitrogen equates to minuscule vegetable yields.

Rhizobia nodules on broad bean roots

This page was last updated by Bernard Preston on 9th February, 2023.

Plants require plenty of nitrogen and, in natural fields and forests it is these bacteria that supply most of the goods.

In modern agriculture this is deemed inadequate, and too much schlep so large quantities of nitrogen are supplied to the soil from fertilizer. However, there is always a but it seems.

This nitrogen is very expensive to produce and transport, requiring large amounts of electrical energy, using the Haber-Bosch process that you probably learned about in high school science.

In nature there are but two sources of the nitrogen; that supplied by these tiny rhizobium bacteria that live inside the roots of certain plants, in particular for us, legumes. Lightning too will generate a lesser amount.

Nitrogen fixation bacteria

Nitrogen fixation bacteria are vital; without them we could not exist. Honeybees have a similarly important role in pollinating the flowers of legumes.

What is biological Nitrogen-Fixation?

  1. Legumes in the garden reduce our reliance on red meat and dairy for our protein.
  2. Legumes are the power-houses where nitrogen-fixation occurs; the gas for all our other plants is utterly dependent on the element in the soil. They are unable to produce their own.

So if you want beautiful lettuce, corn and broccoli, you either have to provide biological nitrogen fixation from legumes or use artificial fertiliser. Or perhaps a bit of both, depending on how fanatical you are about organic farming methods.

Inoculating rhizobia onto legume seeds can make a huge difference to the available nitrogen firstly for these plants but also for the next crop.

Nitrogen fixation is a subject that no wellness and garden-nut can afford to ignore. Fava beans nutrition is a good place to begin; they supply one part of our start to the day for most of the year. What is astonishing is that you have no hunger pangs for the rest of the morning; they give satiety.

Another form of nitrogen-fixation is keeping chickens; they don't pee so the ratio of nitrogen to carbon in their manure is more than double that of a cow, and four times that of a horse.

Biological nitrogen-fixation by legumes

There are some very smart bacteria; billions of good bugs, as well as the pathogens that seek to destroy us. They have an enzyme that can capture the gas from the air and fix it into a soluble compound called ammonia. Remember the atmosphere is 80 percent nitrogen but plants cannot utilize it; nor can animals like us.

Nitrogen is the basis of all amino acids, those vital building blocks of protein; and our DNA too. These bacteria then convert the ammonia into these compounds for their own needs and the host legume.

Then when they die, this nitrogen is released into the soil and becomes available to other plants like your lettuce and maize that need it for their genes; and hence to us for our own building-blocks when we eat vegetables with protein.

Where do legumes come into this? Not all plants can become involved in fixation of nitrogen. Your lettuce cannot, and nor can your broccoli. You and I can not either; but the pea and bean are able to.

Legumes have special nodules on their roots where these unique nitrogen-fixation bacteria find their way from the soil.

Pull out a bean plant and check it out. Do you see all those bumps? That is biological nitrogen-fixation.

You may be wondering what are legumes? They make a huge contribution to what today are considered good brain foods.

Atmospheric nitrogen-fixation by lightning

Atmospheric nitrogen fixation by lightning is the lesser way of nature making the element available to plants, and hence to us.

Every gardener knows too that in some mysterious way, rain associated with lightning is so beneficial to the vegetables. Within days everything is greener, with new shoots appearing; it is all about the formation of nitrogen-oxides and ammonia from the atmosphere. They are highly soluble, making the element available to plants.


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Our own proteins requirements are utterly dependent on the nitric oxides from the arcing effect of lightning.

And the ammonia formed by nitrogen-fixation bacteria; the rhizobia.

Researchers by counting flashes from satellites estimate that lightning releases about 26,000 tons of nitrogen-oxides into the atmosphere every year; that is small fry compared the biological fixation of the element, yet important.

Gardeners have also known for millennia that vegetables planted where last season there was a pea or bean crop, are particularly luscious and bear abundant fruit.

And so gardeners use plant-rotation. A pea or bean will be followed by lettuce or broccoli, for example; and then by a root crop like carrot or onion.

And then back to the nitrogen-fixation of legumes.

This happy, symbiotic and mutually-advantageous relationship between legumes and nitrogen fixation bacteria can make the organic gardener completely independent of synthetic fertilisers.

We can and should use biological nitrogen-fixation to the advantage of the plants and our own food.

Starting a compost pile

Starting a compost pile is the other side of the coin when you are trying desperately to grow nutritious choice foods. Vegetable plants of course need a lot more than just nitrogen.

Whilst biological nitrogen-fixation is a vital gardening practice, so is starting a compost pile for all the other nutrients that your broccoli, carrots and lettuce are going to need. And perhaps, if you love succotash like I do, your first attempt will be at growing lima beans; they are very nutritious legumes for our own protein needs, as well as for their capacity to fix the element for the soil.

Later I will be pulling up some old legume plants; it is the end of summer. We must be careful to save bean seeds for next season, so I will get some photos of the roots so you can see the nodules where these amazing nitrogen-fixation bacteria are so busily engaged in providing for our garden.

Getting your garden soil ready for planting also happens to be a profound way of sequestering carbon in the atmosphere and getting most of it back where it belongs; in the ground.

What is nitrogen-fixation?

Have you got it? It's all about capturing unavailable nitrogen from the atmosphere and making it available for our plants. Even if you do not have a vegetable garden, as such, it is not difficult to plant a few pole beans here and there, or some peas between your flowers. The taste of organically grown veggies is without equal.

Growing Green Beans (bush)

Growing green beans need a compost rich environment.

Growing chickpeas and beans compost.

I have four compost heaps on the go; yes, we have a large African garden. Each year in the spring I'll grow a crop of bush beans in what is left of one of the piles of humus. Once we have reaped the crop, it is lush and prolific, then I just cover the bean plants, nitrogen fixation bacteria and all, to infect the new compost heap with these amazing little friendly bugs.

Do not swallow the claptrap that the banting folk are giving out that legumes are bad for you because of the starches; it is very low GI carbohydrate and does not produce a fattening insulin rush like donuts, delicious white rolls and potatoes do. If you are still unsure, find out more about the meaning of starch.

  • Banting rebuttal

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I photographed these two butternuts this morning, the one in virgin soil and the other, the monster, at least double the size, growing where last year I grew peas. In fact, peas planted in a trench of compost. See the influence of the compost and the effect of nitrogen fixation by the bacteria in the roots of the peas? Growing Butternut Squash.

Butternut small
Butternut compost large fruit.

An aside

Fixation of nitrogen requires a great deal of energy.

These amazingly little bacteria get that energy from the aerobic respiration that provides it for an enzyme called nitrogenase; it converts the gas from the air to ammonia.

Mankind gets that energy in the main from power stations that provide the large amount of electricity required to manufacture nitrogenous fertilizers.

We are of course slowly but surely running out of fossil fuels. One day all of agriculture will rely on biological nitrogen fixation for our food, just like plants have done for billions of years before the arrival of man. Real progress goes backwards sometimes.

Thought of starting to get some of your electricity from solar power energy? I, Bernard Preston, am typing this page in the early hours before dawn on my Apple computer and a 3 watt LED light entirely powered by the sun. Sixteen photo-voltaic panels convert solar energy into electricity stored in four large batteries.

I am trying in some small way to ape those nitrogen fixation bacteria; shall we call it solar fixation? Helping to sustain the planet so that our children will still have a place to live once the world's fossil fuels have run out.

Join me in becoming a environmental freak and being consumed by the need for plenty of energy and vitality, and leaving a wonderful legacy to your offspring.

Bernard Preston

Bernard Preston's books are for all those who are enjoying this site; in part it is your way of thanking me for the huge number of hours going into teaching about choice foods, harnessing the energy from the sun and harvesting the rain. But in part they are spanking good reads. There are free chapters to whet your appetite.

The early morning light is starting to filter through to the PV panels that are now registering 36 watts, enough for a dozen LED lights, but not of course sufficient for my Mac which uses 150W; for that I will have to wait another hour for more intense sunshine.

But the batteries are registering 72 percent charged, so I still have enough electrical power, and a cup of coffee will provide me with the energy to start the editing of Book III of my latest trilogy. The Return of Klein-Jan is complete, but needs a good deal of work, the painful part of being a writer. Update; it is now complete.

Read Books I (The Bostonians) and II (Peter's kids). They are only 99c each; and now Book III (The Return). 

This is the A FAMILY AFFAIR home page; more thought-provoking, inspiring books from Bernard Preston. This a controversial one; be prepared to be shocked.

A Family Affair The Return cover.

Update 1: It is now 8am, and the PV panels are now producing 900 watts, and my Mac is using only 150W. The rest goes into the batteries for storage. Quite soon she who must be obeyed will be starting the bread-maker for our solar bread. That draws 600W, but only intermittently for 50 mins, and by then the sun will be yielding nearly 3kW to our solar panels. More about that on another page. The long and the short of it: there is plenty of energy from the sun if you have the wherewithall to collect it and solar fixate the sun's energy.

Update 2: Sheer greed, those four little panels have grown to fourteen PV panels, enough to produce a steady 2.2kW during the day, peaking over 3kW. Solar fixation. 8am and I have 900W of energy charging the batteries, baking the bread, powering the coffee machine...

solar powered generator

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