Aha! moment about nitrogen.

[Joe Dupre']

Ok, not going the full chemistry route...........just plain facts and common sense.

Trees need nitrogen. 300 million years of evolution on that road.

The air we breathe is about 78% nitrogen. Nitrogen must be pretty important.

Trees in general, don't take up nitrogen directly from the soil.

Basically, trees need bacteria to break down nitrogen of ANY kind into a form they can use.

Organic material is a great home for bacteria.

Bonsai soil needs to be "airy" to promote drainage and to pull air (with that 78% nitrogen) down into the soil.

SO................. for my way of growing bonsai, i.e. promoting growth on less mature trees, a combination of half or less of appropriate aggregate material and the remainder being an airy organic (pine bark) seems to be the best all-around recipe for me in my climate. It seems to have worked for over 150 trees collected from the wild plus a couple of dozen nursery stock plants. That gorgeous nursery procumbens, ficus or azalea you just had to have on your last visit to the nursery was no doubt raised in primarily pine bark or peat moss type of soil. Take that recipe and add a good dose of aggregate for good drainage and you're on your way.

 

[Deleted member 47471]

I like it. The unused nitrogen in fertilizer flushes out easily in aggregate soil also (binds to the smallest bits with water).

 

[Shibui]

Atmospheric N is not available to plants, even when it is 'dragged into the soil' Some bacteria can convert atmospheric N into a form that can be used by plants but they are very specialised bacteria that are only associated with a couple of plant families - Legumes, Casuarina and maybe 1 or 2 others. Even those associations are not as philanthropic as some would believe. Converting N from air is very hard work so the bacteria that do it don't let it go easily.
I'd suggest the 'airy' soil you find so beneficial is probably good for reasons other than N exchange from the air.

 

[Joe Dupre']

Atmospheric N is not available to plants, even when it is 'dragged into the soil' Some bacteria can convert atmospheric N into a form that can be used by plants but they are very specialised bacteria that are only associated with a couple of plant families - Legumes, Casuarina and maybe 1 or 2 others. Even those associations are not as philanthropic as some would believe. Converting N from air is very hard work so the bacteria that do it don't let it go easily.
I'd suggest the 'airy' soil you find so beneficial is probably good for reasons other than N exchange from the air.

So, exactly how do most plants get their nitrogen?

 

[Shibui]

Plant roots can absorb nitrogen in both nitrate (NO3-) and ammonium (NH4+).
A lot of nitrogen in the environment is 'organic' nitrogen where various carbon compounds are bonded with NH2 but plants cannot absorb those compounds directly. They rely on bacteria and other soil life to digest the organics and break the compounds down into NO3 and NH4.
Check out the nitrogen cycle for a rough overview of how nitrogen cycles and recycles from soil and air through plants and animals and back again.

 

[Bonsai Nut]

a combination of half or less of appropriate aggregate material and the remainder being an airy organic (pine bark) seems to be the best all-around recipe for me in my climate

Plants will take up nutrients and minerals in the form that is most readily available. They cannot absorb the nitrogen in pine bark until it has decomposed - through a series of processes where different groups of micro-life act in different ways to break down the bark. In the short term, the bacteria in fresh pine bark that starts to decompose actually absorb carbon and nitrogen in order to break down the proteins and lipids in the bark - producing excess heat that can reach as high as 165F (when composting in a pile). Pine bark decomposes slowly, which is why (when properly graded and sifted) it can be a good soil component - because it can still be present in the soil years after you last repotted. In the meantime, use standard fertilizer with your trees. They will absorb the readily available commercial plant fertilizer long before they start to rely on nutrients from the bark.

You can do a quick search on "the nitrogen cycle" to get a topline of the processes involved in breaking ammonia into nitrites, and nitrites into nitrates.

 

[penumbra]

The loose and airy soil mix is even more important for the free exchange of oxygen, which unlike nitrogen has a highly reactive molecule.

 

[Joe Dupre']

So much for avoiding the chemistry lesson. LOL! Much appreciated, but I like to keep it simple. Airy, organic soil components are not the enemy that many people proclaim. Adding enough inorganic substrate to the soil to promote drainage gives me the best results. Note: Results......not online research, not hearsay, not opinion............... eyewitness results of close to 200 trees of about 30 different species and cultivars.

 

[Glaucus]

Yup, this is actually pretty crazy. nitrogen gas aka N2 has a very strong triple bond, it is a diatomic molecule. Just like Oxygen aka O2 and hydrogen gas aka H2.
Atmosphere is filled with N2 gas. But to break that bond, you need to expend a lot of energy. But if you break it you can make many molecules, like NH4+, NH3 NO-, NO2, NO3-.
Only bacteria can take N2 gas from the air, and make it into nitrogen lego that can be used as a building block for life. But life needs the nitrogen atom to make the most essential things. DNA and other nucleaic acids, organic compounds similar to DNA like ATP, which is the universal energy carrier of life, and also all amino acids. Which are used to create proteins. Without nitrogen atoms, you just have sugars and fats.

It is not that animals are not able to take N2 from the air, and create for themselves all these essential molecules. Even plants can't. Neither can fungi. Only bacteria can (and some archaea but let's consider them 'bacteria'. Just some plants have learned to 'farm' these bacteria for their bioavailable nitrogen. And these are the legumes aka Fabaceae family that can do this, and farm the bacteria for their nitrogen, by creating root nodules. Though there are some plants that are the odd exceptions and that evolved this trait independently, like the alder tree and some in the Rosales order.

Since taking N2 gas and making ammonia or nitrate takes energy, the reverse produces energy. So there are also many bacteria that get energy from using the reverse reaction. So many bacteria in the soils can 'fix nitrogen', others turn ammonia into nitrate and then back into nitrogen gas. And all life is dependent on those bacteria that can fix nitrogen. Every organic molecule that enters your body and contains a nitrogen atom has their origin in some bacteria.

Pretty crazy that after 470 million years of plant evolution, plants still have not 'learned' how to fix their own nitrogen. There is a reason for this which I won't go into right now, but interesting nonetheless. Same for animals and fungi of course, but since most of then usually eat plants, that's less strange. (There is actually one fungi exception that can fix their own nitrogen, though. Didn't know about that. But one of the first things I learned about biology after high school is that biology always has exceptions to everything.)

Actually humans can also create their own nitrogen. Thanks to some smart German scientists who famously also had a hand in the poison gas of WW1. But for this Haber-Bosch process, we need to go to 400 °C/752°F and at least 100 times atmospheric pressure for this N2 triple bond to be broken.. We don't even have an industrial economically affordable method to do it at room temperature and at atmospheric pressure, like nature does.

 

[Desert O'Piñon]

The bacterial aspect is very interesting to me. I don't remember learning that along the way. I do remember hearing about lightning fixing atmospheric nitrogen into nitrates which are then dissolved into raindrops that pull usable nitrogen into the soil. I was told by my grandfather that the smell of rain was caused by this process.