GardenBanter.co.uk - View Single Post

23-11-2004, 06:06 PM

wrote in
:

hey... I went all the way thru quantitative analysis and dissociation
constants (twice yet). what I need is Rod Farley or a real chemist...
isnt somebody's husband a chemist on this list? I done all the
searches and have come up with the standard "total nitrogen" thing,
now I want it explained in more detail and WHY they use this way of
expressing it when they werent doing that 20 years ago when I took the
damn chem course. Ingrid

NO3-N is a term used by environmental chemists as well as (as someone has
already said) in agriculture. It's not new - it was certainly in common
use in the '70's when I was involved in drinking water quality and I'm
pretty sure it dates back to the start of the 20th century or before.

It is used because there can be several different nitrogen compounds (eg
ammonia, nitrite, nitrate or albumoid compounds) which have diffrent
proportions of nitrogen in them. Often it is OK just to express the
concentration of that compound in the usual way - eg mg NH3 per litre, or
mg NO3 per litre. But they contain very different amounts of nitrogen. So
whereas 1 mg NO3 contains only about 0.2 mg nitrogen, 1 mg NH3 contains
0.8 mg nitrogen.

So when the amount of nitrogen is more important than the amount of the
compound it is usual to convert all concentrations to the equivalent
amount of nitrogen. So 1 mg/l NO3-N means 1mg/l of nitrogen which happens
to be in the form of nitrate, and this represents exactly the same amount
of nitrogen as 1 mg/l NH3-N, or alb-N, or NO2-N, etc.

Similarly, if you are spreading it on a field, 1 kilogram NO3-N will
provide the same amount of available nitrogen as 1 kilogram NH3-N.

Hope this helps.

Cuvapu