NPK ratios?

Eugene Zielinski
Sat, 02 Feb 2008 19:41:49 PST
Please bear with me -- I'm trying to remember things from my college days,
and that information has had 30+ years to degrade.  (Corrections are
But, if I remember correctly, soil clay particles have a net negative
charge.  Certain plant nutrients, such as calcium, potassium, magnesium,
and ammonium, have a positive charge.  Thus, these materials would be held
in the soil, bound to clay particles.  Nitrate and phosphate, on the other
hand, have a negative charge.  If not taken up by plants, they would pass
through the soil, to contaminate groundwater, or cause algal population
explosions in nearby ponds, lakes, and streams.  Perhaps this is why high
levels of phosphate are recommended for crops.  Ammonium bound in the soil
may not be readily available to plants, but it could be converted to
nitrate by bacterial action, which plants could then use -- a "long term"
source of nitrogen.
I wonder if fertilizer rates recommended for plants grown in regular soil
have much relevance to those of us who grow/garden in "soilless" media.


Eugene Zielinski
Augusta, GA

> Date: Sat, 2 Feb 2008 18:55:27 -0800
> Subject: Re: [pbs] NPK ratios?
> To: Pacific Bulb Society <>
> On 31 Jan 08, at 9:09, J.E. Shields wrote:
> > Clays can adsorb ions on their surfaces and can absorb [sic; ITYM
> > "adsorb"] ions internally. 
> Not all clays. Lateritic clays have very poor adsorption powers, 
> hence the poor soils in the Oregon Coast Range (Ref: Roadside Geology 
> of Oregon), Africa, and the Amazon Basin.
> -- 
> Rodger Whitlock
> Victoria, British Columbia, Canada
> Maritime Zone 8, a cool Mediterranean climate
> on beautiful Vancouver Island

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