Alex wrote:
"David Hare-Scott" schreef in bericht
...
Alex wrote:
"David Hare-Scott" schreef in bericht
...
David E. Ross wrote:
On 9/14/2009 12:44 PM, Alex wrote:
Hi,

I would like to know what the correct EC is for the potting soil
of various plants.

Is there any website that has this information?

Thanks



What is "EC"?

Electrical Conductivity. Used as a measure of dissolved salts.

David

Right. Most descriptions for plants say 'use a light mix' or
something like that - I want to be precise and know exactly what my
plants
are going to need, and what they're getting, which is why I measure
runoff with an EC meter.


I don't think this will work.

However, it is difficult to find the correct EC (or ppm/parts per
millions) for plants online.


I don't think this will help much, if at all.

So I am wondering if someone has come a across a website
or a book which gives you good information over what to use.

Alex

I am not sure that there is a "correct" EC for each plant. A given
EC is the result of the agregate of the dissolved salts in the
sample but depending on the combination of cations and anions that
make it up it could be suitable or unsuitable for a growing medium.
For example an EC of "X" might be made up of a good balance of salts
supplying all the major and minor elements or the result of just
sodium chloride. Also the presence of certain quantities of soluble
minerals is not a good indication of solid medium fertility as some
quite adequate nutrients may be available as partly soluble
compounds which contribute little to the EC reading. Likewise an EC
in the "correct" range will not tell you if some trace elements are
missing.

My understanding is that EC is used to estimate when excessive salts
might be present. The higher the EC the fewer types of plants that
will grow in it assuming that the correct elements are present. Thus
it can assist in saying if medium is unsuitable (the EC is too high
for the plant to tolerate) but cannot say if it is suitable (the
correct balance of nutrients are available). For example plants
adapted to growing in salt pans etc can tolerate a much higher EC
than others.

The reason I have qualified what I have said here is that I don't
use EC in growing and I am speaking from theory. Do you have a
reference that says that EC can be used the way that you describe?

David

The reason I think using EC as a measure of required nutrient strenght
or flushing, is that

1) Short of soil testing, you can use runoff as an indication of what
is going on in your soil

No you can use it as an indication of what is running off, that doesn't tell
you what is left. Soils have a huge variation in ability to bind ions. I
could give you four pots with quite different EC and this would tell you
little.

A: high EC due to NaCl = very bad for growing
B low EC due to low minerals in all forms = bad for growing
C high EC due to runoff of a soluble balanced mix of nutrients = could be
good or bad for growing depending on what is left, very wasteful anyway
D low-medium EC due to little runoff of soluble ions but adequate bound
nutrients = good for growing



2) EC is much more precise a measure than the usual 'use 2 ml per
liter' when it comes to nutrient solution

I cannot see how this helps, are you talking about measuring fertiliser
solutions? Why? If you really want to get accurate measure of solutes then
weigh them. I doubt that you need such accuracy.

3) EC is very important in hydroponics, so why shouldn't it be
in soil or oranic growing media?


Because in hydropnics all your nutrients are in solution in real soil they
are not, this is key idea which you seem to have missed. Also hydro
solutions are less stable than real soil so they need closer monitoring.

It cannot tell you how much of a specific nutrient is
available/missing,
but it can give you clues about how much to use.


Maybe. I doubt it.

So I just have to wonder - what is the optimal EC for soil of
various plants?


I don't see how the concept of a particular EC for a given plant is
meaningful much less useful.

I haven't found a lot of literature dealing with this.


That could be because it is not used in that way in practice.

Overall I suspect you are heading a blind alley. I suggest that you learn
to build good soil and how to monitor the health of the soil by what it
produces which is far simpler in the end. Soil is a very complex medium and
we don't yet understand all its working in detail so trying to model the
system by measuring just one aspect is pointless in my view.

Once more let me say that I have not gone down this path myself so I am not
speaking from experience but I have given reasons why I am doubtful.


David