jackrowe at compuserve.com
Tue Sep 16 14:09:18 EDT 1997
That's an interesting question, which I'm going to throw some guesses at...
As far as phosphorous/phosphates, these are considered "immobile" in soil,
which means that as soon as they dissolve (which is gradually) they are
electrically-bonded or "adhered" to soil particles and so don't leach away
readily. However, by picking up the adhered soil particle itself and
washing IT away you can still loose the P by erosion (a common practice,
actually, if you till or dig, are on a slope, don't mulch, etc). According
to US's National Research Council's "Alternative Agriculture", 1989,
average soil losses in US are 1-1/2 to 13 tons per acre per year. 1-1/2
tons (limited tillage, level grade) is 2 - 3 TBS./sq foot/yr; 13 tons
(tilled, 8% slope) is near a cup. Wacky practice.
Other minerals are typically more soluble, to varying degrees. Potassium,
for instance, is pretty soluble and can be leached by rain, erosion aside.
Not much point in washing away soluble minerals in winter, unless you are
growing crops then (perfectly possible in the US's Pacific Northwest, or
here in the Deep South), or using grass/etc as a catch crop to chelate
minerals into plant-food form. Really, if you can grow veggies, grasses,
mustard, etc. during your winters this is a really good practice in any
case, because a lot of soil nitrogen is typically lost during winter
Since most rock powders act over 3 - 4 years, all this is probably
happily-close to moot. In a good organic soil, rock powders can become
reasonably available pretty quickly. By the way, a soil test will show, on
the average US farm/garden, a surfeit of (expensive) phosphorous -- doesn't
take much (NRCs Alt. Ag. again...).
Sad Note... the innocent-sounding term "immobile in soil" is a sobering
example of the profound depth to which the paradigm of "modern agriculture"
has penetrated in just 60-odd (damn odd!) years. Astute organic gardeners
will instinctively ask themselves -- thinking of the living, breathing,
moving/wriggling conglomeration they know and love as "soil" -- How can P
be immobile in soil which is, itself, mobile?. In Modern, a.k.a.
Hydroponics-in-Dead-Dirt, Agriculture, nation-sized quantities of food
are grown across vast acreages of soil which JUST LAYS THERE. Dead soil
(wish 'twer an oxymoron!). Hopefully not extinct, yet. Endangered perhaps,
A mind is a cyclical opportunity in space/time. Grab it!
More information about the permaculture