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Brew Mix for Plants?
Rachel asked about using compressed CO2 + N2 (Brew Mix) in place of
compressed CO2 (as a source of C) and KNO3 (as a source of both K and N).
It won't work.
The nitrogen in Brew Mix (and the majority of the nitrogen in the
atmosphere) exists as stable molecules - two atoms of Nitrogen bound
together by a triple bond into N2 molecules. The triple bond is very stable
and causes the molecule to be inert (non-reactive) at normal temperatures.
The don't do much of anything other than bounce around and contribute to air
pressure. It takes exceedingly high temperatures (such as found in a bolt of
lightening or inside of an internal combustion engine) or "nitrogen fixing"
bacteria to break these bonds.
The following is based on material in Mineral Nutrition of Higher Plants,
2nd ed., by Horst Marschner, 1995 Academic Press.
Plants absorb all but one of the essential mineral nutrient as ions,
electrically charged "parts" of molecules, not as complete electrically
neutral molecules. Boron is the only essential element which enters a plant
as part of an electrically neutral species - B(OH)3
Nitrogen is taken up by plants either as the anion NO3- (nitrate) or the
cation NH4+ (ammonium). Both nitrate and ammonium must be reduced and
assimilated into organic compounds before the nitrogen they contain can be
encorporated into plant tissue.
Nitrate --> nitrate reductase --> Nitrite --> nitrite reductase --> Ammonium
+ glutamate --> glutamine synthase --> Glutamine.
Glutamine may then undergo additional transformations before entering the
xylem flow as reduced N, depending upon the plant species.
So, plain, ordinary, Nitrogen gas just won't cut the mustard, so to speak.
Some plants grow in association with certain species of "nitrogen fixing"
bacteria and these bacteria ARE capable of taking Nitrogen directly from the
atmosphere and passing it to the plants in a form which they can use.
Legumes (beans, peas, etc.) are the most widely known plants which live in
such association and among aquatic plants the aquatic fern Azolla has
"nitrogen fixing" bacteria in its tissue, so it derives at least some of its
Nitrogen needs from the bacteria.
Enjoy the beer, but pass on the bottled gas.......except as a source of