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Re: Chemistry questions, N,P,K ratios

> From: TomWood3 at aol_com
> Subject: Re: Chemistry Questions: N-P-K Ratios
> It looks like K2HPO4 starts out with the lowest amount of
> P.  If I measured out the right proportions of that, and then added the
> appropriate amounts of KNO3 and K2SO4, based on these percentages, can I mix a
> solution with a known N-P-K ratio?


> I'm planning on using a huge hypodermic
> syringe to inject this deep into the substrate where, theoretically, the
> cation exchange sites in the clays and vermiculite I've added will hold these
> nutrients out of the water column.

	I don't know why one would expect _cation_ exchange sites to keep
nitrate, sulphate or phosphate (anions) out of the water column.  They
would probably not be too efective at hanging on to potassium (single
charge) either.  In practice, I suspect that the iron oxide-based substrates
just _might_ hang on to phosphate, and have voiced that suspicion here 
before.  I would not be surprised if that is the main function
of laterite.  Nitrate is almost always very mobile, and sulphate usually
is as well.  Injecting trace elements into a substrate with high CEC
might result in the Fe, Mn, Zn and Cu being retained there, but the
chelating agents could prevent that - that is what they are supposed to do.

Paul Sears        Ottawa, Canada