On Sat, 22 Mar 2003 23:51:42 +0000, m wrote:

I did a lot of research, a summary of which is presented below with a few
relevant links for those who wish to do their own follow-up research. My
conclusion is that your subject line was misleading and is unsubstantiated
by the facts. The research material I found did not relate to
over-fertilization. At all.


I went he
http://www.fuzzylu.com/greencenter/q36/ghupdate.htm

and reading just the first few paragraphs of the article, I notice that
there were some very unusual circumstances.

"the low light levels characteristic of the winter greenhouse cause leafy
vegetables to accumulate potentially unhealthful levels of nitrate, even
when soil N is not excessive (NO,) (Schonbeck 1987 and Schonbeck 1988)"

But then I kept reading the whole article and found:

A) The results are weather dependent and that means that they are latitude
dependent (the test was conducted in Massuchusetts, USA). Moreover, they
can not be duplicated because the weather is not a controllable element in
this study.

B) a "potentially unhealthful" level of something does not mean it is
poisonous in normal useage.

C) there was no supplemental lighting used

D) the plants were being grown for the rooted plant gardening trade and
would be hardened off out doors prior to sale. Thus, the level of nitrates
would be corrected before consumers had contact with the plants.

D) the bulk of 'the problem' within the greehouse was solved through the
use of organic scrubbers.

This study is, at best, incomplete and makes no mention of
overfertilization, in the greenhouse or elsewhere.

..

for the mustard arsenic issue....

+mustard+phytoremediation+arsenic

From here ( http://abstracts.aspb.org/aspb1998/41/0443.shtml ) we get:
"Arsenic uptake and transport was examined in hydroponically grown
Brassica juncea (Indian mustard) under microbial controlled conditions. By
using radioisotope 73As, the kinetics and pattern of As uptake by plant
roots were investigated. Arsenic uptake by plant roots was affected by
conditions such as solution pH, phosphorus concentrations and
reducing/chelating agents."

In English:
If we try really, really hard, we can get mustard to take up arsenic from
a solution. What we can't do is get the tractor to walk on water to plant
the darned stuff.

Moreover, this study was based on hydroponic conditions ... totally
isolated from field conditions. It used externally sterile seed. This
would never occur in the field.It used carefully controlled growing
conditions. This would also never occur in the field. It grew the seeds in
a water solution. This would never occur in the field.

It is absurd to try to map these experimental results to field conditions.
They just won't make the jump.

From here http://www.plantphysiol.org/cgi/reprint/122/4/1171.pdf we get
the acknowledgement that the bulk of the arsenic is stopped in the root
tissue UNLESS dimercaptosuccinate is added to the soil / solution.

Moreover, on page 4 of this study there is an indication that adequate
amounts of phospates inhibit the uptake of AS. Which is to indicate that
plants growing in a balanced media / on healthy soil pose no risk. In the
preface to the study there was an acknowledgement that small amounts of AS
are actually beneficial to animal metabolism. People are animals. In the
Discussion section on page 6 there was an acknowledgment that, without
adding dimercaptosuccinate as a chelating agent, the uptake of AS to the
edible parts was of no real consequence but that after adding the chelate,
while the total amount of AS absorbed into the plant remained relatively
steady, a larger percentage of it moved to the shoots where it could be
harvested.

IF such bioremediation were put into place in the field, then the AS in
the harvested shoots would be neutralized, quite possibly by composting /
aging. Once bound into biologically unavailable (or only slowly available)
compounds, the quantity of a poison in a soil is irrelevant to its uptake.


The conclusion I reach is that, if you are REALLY worried about this,
don't add dimercaptosuccinate to your soil when growing Indian mustard.

Contrary to your subject line, I don't see any mention of
over-fertilization. Do you?

Your subject line is speculative and unsubstantiated.



moral of the story....there are subtleties, even in gardening

The moral of the story is that it is important to read a scientific study
closely before arriving at a conclusion.

In the case of the AS, what happens if dimercaptosuccinate ISNT added to
the solution? Pretty much nothing of significance. What happens if it IS
added to soil? Impossible to know, this study did not measure that.

Here's my take on the results. A way has been researched in which it is
possible to influence the uptake of AS in a carefully controlled manner
unduplicable in nature. Would you care to argue otherwise?