Chemistry 101

Burger, Steve
Wed, 09 Nov 2005 09:05:14 PST
More on soil chemistry... This is also a response to some of the dialogue around granite dust among other recent related posts.

The organic movement advocates a lot of sources of nutrient of disputed value. I don't imagine I would rely on granite dust, for instance,  as anything but a minor supplement unless I could spread truckloads of it over my .5 acre garden.  It was said in a previous message that it was released in the ppm range, but K is not a micro nutrient, and some plants feed quite heavily on it.  I could see granite dust as helpful to prevent "crashes" in nutrient levels between soluble fertilizer uses, perhaps.  I would lump this in with green sand and phosphate rock, among others, suggested by some in that community.  These are minerals that don't give their nutrients up too readily.

As a medium for growth (pot culture), the relative inertness of granite dust and some of these other products probably lends more to their usefulness than do any of their chemical properties, and I have no doubt they are probably useful in that application.

As for inorganic sources of nutrient(oddly, granite, sand and phosphate rock are technically inorganic, but that's another story), soil chemistry and the chemistry of the fertilizers themselves play a huge role in how useful they are.  For instance if the pH is too high, even soluble forms of Phosphate can be bound in the soil.  Some fertilizers have a high salt index, and some have carriers we need to pay attention to.  Potassium nitrate, if I recall correctly from University, has a terribly high salt index (a measure of equivalence to NaCl I think).

In the end, our plants need X,Y and Z (N,P and K and more) to grow and they get to the plant in the soil solution the same way, whether we're using organics, minerals, or inorganic salts.  How we go about getting there is as much a matter of preference and experience as it is science.  For me $s and effort matter most.  So I practice good use of soil amendments, and I use the cheapest products that get the job done for me.  I expect no miracle from any product I try.

BTW I'm no chemical junky, I try to use the safest thing at my disposal, whether it be pest control or fertilizer.  Cost plays a big role here as does ready availability.  Also, other parts of the organic movement's practices are excellent.  Incorporating large amounts of organic matter, being mindful of soil microbes and macrobes, are all sound and do a great deal to assist those of us with poor soils.


-----Original Message-----
[]On Behalf Of Rodger Whitlock
Sent: Tuesday, November 08, 2005 11:36 PM
Subject: Re: [pbs] Chemistry 101

On  8 Nov 05 at 14:13, J.E. Shields wrote:

> Chemistry 101 note:  pH is the hydrogen ion potential, or
> acidity.  pH 7 is considered neutral (neither acid nor
> alkaline) and is the pH of ultrapure water.  pH values below 7
> are considered acid, while pH values above 7 are considered
> alkaline.

But for horticultural purposes, pH 6.5 is considered neutral.

(Now that we've got them all completely confused, you hold 'em 
while I steal their wallets.)

Rodger Whitlock
Victoria, British Columbia, Canada
Maritime Zone 8, a cool Mediterranean climate

on beautiful Vancouver Island
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