Organic vs inorganic PO4, NO3? - Fertilizing

Laith · 11-03-2005, 12:04 AM

Maybe somebody can clarify something for me. I keep reading about the differences between organic and inorganic PO4 and NO3.

I'm still trying to get my head around what exactly the difference is. I mean as far as I remember from chemistry, PO4 is PO4 is PO4 is PO4... and the same for NO3.

Is the PO4 bonded to different elements when its called organic versus inorganic? Perhaps the organic has a Carbon atom attached or something while the inorganic does not? I mean there must be a difference in the chemical composition to justify the different impacts on plants/fish that are talked about...

Mnemia · 11-03-2005, 08:17 AM

I believe you are correct.

Check this out: http://en.wikipedia.org/wiki/Phosphate

That says that "inorganic phosphate" refers to what we normally think of and dose, which is phosphate in the ionic form. It says that "organic phosphate" simply refers to phosphate stored in a biological molecule, such as ATP (major energy carrier in biological systems).

Laith · 11-03-2005, 10:10 AM

Excellent! many thanks!

So basically this means that in the water column we will have free phosphate ions (inorganic phosphate) as well as organic phosphate in the form of phosphate bound in DNA and what are basically proteins?

So the plants can only/more easily use the inorganic phosphate?

Are we talking a similar story with the organic and inorganic NO3?

imatrout · 11-03-2005, 10:57 AM

I have also seen threads stating that common hobby test kits only measure organic (un-usable by plants) PO4. Does anybody have information that confims this or suggests otherwise?

Milan · 11-03-2005, 07:18 PM

Quote:

Originally Posted by imatrout

I have also seen threads stating that common hobby test kits only measure organic (un-usable by plants) PO4. Does anybody have information that confims this or suggests otherwise?

In my mind, this is completely incorrect. Firstly, PPS calibrates tests against KNO3 and PO4, so THEY DO MEASURE inorganic form. Secondly, in the past most of the tanks completely relied on organic source of PO4 and NO3, so IT IS USABLE by plants.

defdac · 11-04-2005, 05:44 AM

Quote:

Secondly, in the past most of the tanks completely relied on organic source of PO4 and NO3, so IT IS USABLE by plants.

Only if the substrate contains mineralization-bacteria that converts the organic PO4/NO3 (DOP/DON) to inorganic PO4/NO3 (DIP/DIN).

So fish poo DOP/DON will essentially only contribute to plants via microbial activity, which may or may not be present.

That's why big wc:s that removes DOP/DON with new high inorganic DIP/DIN-levels often is a more sure way of good growth than relying on bacteria that may or may not be present for the most part in the substrate.