Re: [APD] old soil substrate

["Jim Seidman" <js5 at seidman_net>]

Scott Hieber writes:
>>But then using one coffee can's worth instead of 20 ought to be good for
one year to five years instead of twenty to one hundred years? ;-)

If the soil suppplies decades worth of material, then it seems that the
idea with the soil is to have a superabundance of the chems, but "sealed"
down under the gravel. If so, how much one uses doesn't seem all that
critical. Almost any amount is too much but hat's okay because it's
"sealed" as a *sub*strate.

Perhaps the fizzing out is due to lack of fish food.<<

You put a smiley on it, but yes, a coffee can's worth of soil might have a
year's supply of boron. Of course, plants cannot live on boron alone. As I
mentioned, soil is usually a fairly poor source of macronutrients,
especially N.

Walstad's method, at least as I interpret it from her book, has you feeding
enough fish food that it can provide essentially all of the nutrition the
plants need. The soil is useful because it provides a reservoir for these
nutrients. Thus it should work even if the soil only contains, say, a
6-month supply of a given nutrient. At any given time much of a particular
nutrient is not bioavailable. Thus the fish waste slowly replenishes the
substrate. 

If you don't feed enough, the soil will become depleted. How fast this will
occur depends on how much you feed.

The fact that Josh got over a year out of a coffee can's worth of soil in a
50 gallon shows how great soil is at paving over problems. If he had used a
1" layer, he'd probably have gotten years of great growth. If he had used
no soil at all, he probably would never have gotten good plant growth
without fertilizers.

In short, soil is so cheap that you can afford to use a lot. And using a
lot means that you can have many years of success even if your fish food is
low in some nutrient. 

- Jim


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