Re: CULT: fertilizer - long & technical

Gerry Snyder wrote:
> I have certainly heard and read that organic nitrogen (ammonium
> something-or-other) is capable of burning because of being available too
> rapidly, but that mineral nitrogen (nitrate) was much slower to dissolve
> and seldom dangerous in any concentrations (in our sandy soil, that is).
> 
> Any chance you flip-flopped the two kinds?

You are certainly correct about ammonium ions being bad for plants -
let's see if I can remember the details of how this works without
looking it up.  Both ammonium and nitrate are soluble in water. 
Ammonium is a cation (positive charge) and nitrate is an anion (negative
charge).  Although some plants can safely utilize ammonium (mostly
members of the heath family - think blueberries, azaleas, etc and
ammonium sulfate; also conifers), ammonium running around loose inside
the cells of plants is generally toxic.  I can't recall what the plants
that prefer nitrogen in this form do with it to keep from killing
themselves with it, but they have some way of converting it to something
they can use inside the cells.

Organic sources of nitrogen can also have free ammonia (not the ammonium
ion) - you know, the fragrance of urine - ammonia gas - that will burn
the outside of the plant without bothering to waste time getting into
the cell sap.

The plants that tolerate (use) nitrogen as ammonium are ones that grow
in strongly acid soils.

Water moving thru soil usually is more or less acid (think acid rain,
tho rain with a lot of particulates can be slightly basic) - carbon
dioxide in solution in the rainwater forms carbonic acid.  Here's where
I need the book to refresh my memory on how this all works, but nitrate
is a single charge (NO3-) and is smaller than most of the other anions
(??) (SO4-..is the only other one I can think of at the moment).  So it
is easily grabbed by roots (smaller ions fit thru membranes easier than
bigger ones).  However, if there is more in solution at any given time
than the plants can absorb or the exchange surfaces on clays or organic
matter can grab, it will just move with the water out of the bottom of
the soil column.  

Ammonium on the other hand, while highly soluble, is also readily
converted to nitrate or can be turned back into nitrogen (the kind in
air) and go back into the air.  People spend their lives studying this
stuff, mostly because nitrogen dynamics are so fascinatingly
complicated, but I forget all the details...Usually (except in very acid
soils), ammonium is converted to nitrate by bacteria (nitrifying
bacteria - they even have a group name!) before any plants have a chance
to get to it.  Most fertilizer nitrogen is in the form of
ammonium-nitrate (NH4NO3) (or at least it used to be, & I haven't heard
it's changed), so it has both ammonium AND nitrate.  For all practical
purposes, the ammonium is mostly converted to nitrate, then does
whatever.  some of it may go the other route and wind up as NOx (nitrous
oxide - NO2 mostly) and go back into the atmosphere.  EXCEPT in very
acid soils, where ammonium can persist.

Urea is another form of nitrogen used for fertiliser - sort of like two
ammonium ions stuck together.  It is (completely?) insoluble and has to
be broken down by bacteria (?) in order to become either nitrate or
ammonium - so it is neither toxic nor rapidly leached out by rain.  Also
more expensive to manufacture.

Well, that was more than ANYBODY wanted to know.  Hope this overly
simplified explanation makes sense.

Linda Mann east Tennessee USA zone 7/8
SDBs with blooms open turned to mush, but too soon to tell if remaining
buds are damaged.


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