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.
However, it is difficult to find the correct EC (or ppm/parts per millions)
for plants online.
So I am wondering if someone has come a across a website
or a book which gives you good information over what to use.
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?
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
2) EC is much more precise a measure than the usual 'use 2 ml per
liter' when it comes to nutrient solution
3) EC is very important in hydroponics, so why shouldn't it be
in soil or oranic growing media?
It cannot tell you how much of a specific nutrient is available/missing,
but it can give you clues about how much to use.
So I just have to wonder - what is the optimal EC for soil of
I haven't found a lot of literature dealing with this.
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
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
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.
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.
Maybe. I doubt it.
I don't see how the concept of a particular EC for a given plant is
meaningful much less useful.
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.
On Tue, 15 Sep 2009 15:27:03 +1000, "David Hare-Scott"
So from a given number you are measuring ion concentrations, and that
alone doesn't tell you much.
I have a west-coast pad cactus which its mother plant happily lived
and flowered on a salty beach of Pales Verdes. It has been living
with me for 20 years, grows new pads each year, never flowered.
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