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Re: [APD] old soil substrate
Scott Hieber writes:
"Based on Walstad's excellent treatise, doesn't it take many years for the
soil to be depleted?"
Aren't soils from diff places very diff?<<
As Ellen said, a coffee-can full isn't much. Actually, Walstad explicitly
makes the point that you can use much more soil (on a volume basis) than
you can many substrate additives, so even if it's a less concentrated
source of a particular nutrient you still wind up with more.
That said, Walstad expects the soil to be a great source of traces, not
macronutrients. I think that Josh Bjork's problem is limited
macronutrients, which in the Walstad method would be provided by large
amounts of fish food.
As to the differences in soils, Walstad specifically recommends using
topsoil from a well-drained area. While the specific composition will vary
a lot, any topsoil capable of supporting terrestrial plants will of
necessity have certain nutrients in it. Getting it from a well-drained area
also tends to limit how much OM it contains. So yes, soil X may have a 20
year supply of boron while soil Y has a 100 year supply, but either one
would grow plants for a good long time.
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