permaculture

["Wordgarden" <wordgarden@iinet.net.au>]

G'day Rain:

> There were a couple of points I'd like to "correct:"

I stand corrected.

Especially on point 2. On reflection, if plants were not able to mine
out certain elements, then there wouldn't be the current interest in using
certain plants for bioremediation of contaminated sites [the plants absorb
the heavy metal or whatever, and then are pulled up and removed, along with
the heavy metal]. So, I am wrong,
plants *can* strip out elements. And if whole plants are removed then there
may be a loss of nutrients.

On point 1. I agree that municipal sludge need not be nasty. If the waste
stream is properly
designed AND properly used in the way it is designed (i.e., people don't put
their sump oil down the drain). I guess that sewerage systems differ
according to locality, but where I am, the sewers carry household sewage,
and stormwater is handled differently. I think the current system would work
as designed, as far as soil nutrients go, if the sewage wasn't contaminated.


It is "common knowledge that soil fertility declines after only one
to three seasons of exporting crops",
But looking at two examples (potatoes vs. apples) gives an inkling that it
might not always be so: If you
try exporting potatoes [in the normal commercial way] from the same plot
without any proper [not that I
know what is proper] management then productivity will certainly decline.
[loss of soil structure? no soil organisms? build up of disease by lack of
crop rotation?]
But you can export apples for many more years and the fertility doesn't
decline in the same way.

So maybe it depends on how much of the plant is exported and how much stays
on
site? As well as on the farming practises themselves--whether soil is built
or damaged .

I suggest that it is the farming practises themselves
that destroy soil fertility, rather than actual loss of the elements from
the
soil that results in the "common knowledge" decline of fertility--the
elements are probably still there, but the pratice make them unavailable. .
. although plants *can* mine the soil.

I still believe that correct farming practise will keep nutirents available
to plants, and that insignificant amounts are actually exported.

This is belief, though, not tested.

I am just an optimist at heart :)

--Robert