From: Lawrence.London@bbs.oit.unc.edu (Lawrence London)
Subject: Re: Rock dust (was Perelandra, was Whole Earth)
Keywords: gardening Findhorn Perelandra
Organization: Extended Bulletin Board Service
Date: Fri, 21 Aug 1992 03:40:26 GMT

In article <hank.714107921@well.sf.ca.us> hank@well.sf.ca.us (Hank Roberts) writes:
>I'd also like to hear more about uses of rock dust/rock flour for agriculture
>(the idea keeps coming up).  I'd suppose that the rocks _needed_ are the
>rocks not generally found in that locality, so you'd haul stuff in?
Not necessarily. It would depend on the type of rock and what its trace
mineral components were and whether it weathers naturally into finely
granulated soil particles or not. Its always a good idea to add rock powders
from other locales too. Rock or colloidal phosphate and New Jersey Greensand
(Montmorillionite clay) are indespensible and they are available only from
certain locations in the U.S. Generally speaking nearly all rock quarries
that pulverize local stone for construction purposes offer a fine
aggregate known as "screenings". Its usually a mixture of fine silty
particles with fine sand and coarse sandy particles. This will usually weather
in your garden to its mineral components after exposure to the eroding
effects of carbonic acid in decaying biomass and other forces. I think
certain fungi manage to erode rock particles. A good case for careful
stewardship of the land and good natural farming practices and management.
In North Carolina I have access to the following rock powders and would
use them all in large quantities if I could but afford to have them hauled
to my farm:

pyrophyllite screenings - contains potash and trace minerals - has unique
drainage and water retention properties - is an EXCELLENT seed starting
and potting medium, esp. when mixed with organic matter

high-calcium limestone rock (has a higher calcium/magnesium ratio than
dolomitic agricultural limestone - "aglime"

granite screenings - high in potash and trace minerals - "Hybrotite"
hybrid granite from Lithonia, Ga. is especially high in K and trace minerals

rock phosphate - slow-release but high analysis natural phosphate -
colloidal phosphate from Florida is "soft phosphate with colloidal clay"
and is quick release but contains less P

bluestone (I think this may be basalt) - from construction stone quarries -
excellent as a soil conditioner - contains trace minerals & maybe some K


All of these products exert a tremendous texturizing effect on soil.
Plant growth is greatly enhanced. Predatory insect damage on plants grown
in soil fertilized with these materials can conceivably be greatly reduced.
A balanced garden fertilization program should be implemented. Rock based
sources of P, K and micronutrients along with compost, manures and other
natural sources of nitrogen applied according to a regular schedule can
build and sustain production in any cropland. Heavy nitrogen application
without accompanying balanced application of the other nutrients and
micronutrients is a practice to be avoided. Corn and certain other crops
obviously need extra N to bear fruit.  
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