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Old 21-03-2003, 10:08 AM
Tony
 
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Default Too much fertilizer makes vegetables poisonous?

I read somewhere that too much fertilizer can accumulate in leafy vegetables to
the point of being toxic for human consumption, does anyone know where I can
find out more about this, especially as it relates to hydroponics? I read this
in a book on green houses, it said something about problems with nitrogen not
being used up by the leafy vegetables in certain times of the year and thus
accumulating in the edible parts of the vegetable.

-Tony


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Old 22-03-2003, 06:44 AM
mdk-bill
 
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Default Too much fertilizer makes vegetables poisonous?

Tony wrote:

I read somewhere that too much fertilizer can accumulate in leafy
vegetables to the point of being toxic for human consumption, does anyone
know where I can find out more about this, especially as it relates to
hydroponics? I read this in a book on green houses, it said something
about problems with nitrogen not being used up by the leafy vegetables in
certain times of the year and thus accumulating in the edible parts of the
vegetable.

-Tony


Nitrogen is poisonous? In the quantities a plant can pick it up? Hmmmm

I suspect that whatever you were reading might have been classified as
garden F.U.D.

Bill
--
Do not respond to the email address above. It is a fake.

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Old 22-03-2003, 08:56 AM
Tony
 
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Default Too much fertilizer makes vegetables poisonous?

I read somewhere that too much fertilizer can accumulate in leafy
vegetables to the point of being toxic for human consumption, does anyone
know where I can find out more about this, especially as it relates to
hydroponics? I read this in a book on green houses, it said something
about problems with nitrogen not being used up by the leafy vegetables in
certain times of the year and thus accumulating in the edible parts of the
vegetable.


Nitrogen is poisonous? In the quantities a plant can pick it up? Hmmmm [..]


Most likely he was talking about nitrogen in the form fertilizers supply
it, i.e., nitrates/ammonium.

-Tony
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Old 22-03-2003, 05:56 PM
zxcvbob
 
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Default Too much fertilizer makes vegetables poisonous?

mdk-bill wrote:

Tony wrote:

I read somewhere that too much fertilizer can accumulate in leafy
vegetables to the point of being toxic for human consumption, does anyone
know where I can find out more about this, especially as it relates to
hydroponics? I read this in a book on green houses, it said something
about problems with nitrogen not being used up by the leafy vegetables in
certain times of the year and thus accumulating in the edible parts of the
vegetable.

-Tony


Nitrogen is poisonous? In the quantities a plant can pick it up? Hmmmm

I suspect that whatever you were reading might have been classified as
garden F.U.D.

Bill



It was probably extrapolated information from certain grasses (like
sorghum and johnson grass) developing toxic levels of nitrates; toxic to
cattle and horses, which are herbivores.

It is certainly plausable that green leafy vegetables could pick up
toxic amounts of nitrates -- if your diet consists of nothing but those
greens every day.

Even if it's true (and I suspect it's partially true), I have more
important things to worry about.

Best regards,
Bob
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Old 23-03-2003, 12:08 AM
 
Posts: n/a
Default Too much fertilizer makes vegetables poisonous?

On Sat, 22 Mar 2003 08:53:58 GMT, Tony wrote:
I read somewhere that too much fertilizer can accumulate in leafy
vegetables to the point of being toxic for human consumption, does anyone
know where I can find out more about this, especially as it relates to
hydroponics? I read this in a book on green houses, it said something
about problems with nitrogen not being used up by the leafy vegetables in
certain times of the year and thus accumulating in the edible parts of the
vegetable.


Nitrogen is poisonous? In the quantities a plant can pick it up? Hmmmm [..]


Most likely he was talking about nitrogen in the form fertilizers supply
it, i.e., nitrates/ammonium.


here's some info on the proiblem which is quite real. you might also want to
consider the fact that mustard will accumulate arsenic in soils where it is
plentiful.

************************************************** **********************

[1]Web Site Index
[2]New Alchemy Quarterly, No. 33

Nitrate in Winter Greenhouse Leafy Vegetables

Fall, 1988

In recent years, people are eating more fresh vegetables than in the
past, and supermarkets have responded by providing a wide range of
vegetables year-round. During winter and early spring in the
Northeast, these vegetables must be trucked in from farms in
California or other distant locations. Freshness and nutritional
quality may suffer during the long trip, and the fuel consumed exceeds
several-fold the energy value of the food. Also, conventional
vegetable production often entails considerable use of pesticides,
which may leave potentially hazardous residues in the produce. For
example, the Food and Drug Administration detected pesticide residues
in one-third of the lettuce samples and one-half of the tomato samples
it tested between 1982 and 1985.1 Finally, some of our winter fresh
vegetables are grown in Chile and other developing countries where
land and labor are exploited to produce export crops while their
people go hungry.

For these reasons, growing winter vegetables locally in greenhouses
may be an important component of a sustainable regional agriculture
for the Northeast. Throughout its history, New Alchemy Institute (NAI)
has experimented with winter vegetable production in several solar
greenhouses and one compost-heated greenhouse. Leafy vegetables, such
as lettuce, spinach and Chinese cabbage appear most promising, since
they grow well under the low light and low temperature conditions of
the winter greenhouse. Several small commercial greenhouses in New
England are producing lettuce and other greens, and some other growers
are considering winter greenhouse vegetable production. Such produce
is much fresher and more nutritious than trucked-in vegetables, and
few Or no pesticides are used in growing them.

Unfortunately, leafy vegetables grown under winter greenhouse
conditions tend to accumulate nitrate to potentially unhealthful
concentrations. At New Alchemy Institute high nitrate concentrations
were first detected in leafy vegetables grown in our composting
greenhouse, where the soil had been grossly overfertilized by ammonia
from manure in the composting chamber.2 However, we also found high
nitrate levels in leafy vegetables from our two solar greenhouses, and
one commercial solar greenhouse, whose soils received only moderate
amounts of nitrogen from organic sources. Library research revealed
that nitrate accumulation in winter-grown leafy and root vegetables is
a widespread and well-known problem in Europe, where several countries
have legislated maximum allowable concentrations of nitrate in
produce^3 (see Table One).
[3]table 1
Excessive dietary nitrite may cause a life-threatening hemoglobin
malfunction in infants, and may be converted to carcinogenic
nitrosaminos during digestion, posing a possible cancer risk for all
ages.4 Although the extent of this cancer risk is unknown, vegetables
are the main source of dietary nitrate, and researchers agree that
efforts to lower nitrate levels in leafy vegetables are warranted.5

Studies in Europe^5 and in the U.S.6 have identified two major factors
in nitrate accumulation. First, low light levels, such as occur in the
winter greenhouse, retard nitrate utilization by crop growth
processes. Second, heavy application of nitrogen fertilizer increases
uptake of nitrate by the crop. In either case, the excess nitrate
accumulates in the leaves and stems.

During the winter of 1987-88, NAI undertook a nitrate study on
greenhouse lettuce to assess the extent of the problem in New England
and to attempt to identify crop varieties and/or cultural practices
that reduce nitrate levels. In late winter, we harvested six heads of
butterhead type lettuce from each of seven greenhouses in southern New
England, including our own composting greenhouse, and measured their
nitrate concentrations. With one exception, the greenhouse lettuces
contained mote nitrate than did California field-grown butterhead
lettuces purchased at a local supermarket (Table). The lettuces from
greenhouse 7 had not received a fertilizer application for several
weeks before harvest, and appeared nitrogen-deficient. The reason that
lettuce from greenhouses 5 and 6 had somewhat less nitrate than the
four hydroponic greenhouses is not clear, and no conclusion can be
drawn regarding the tendency of soil,' integrated aquaculture or
nutrient solution culture to cause nitrate accumulation. However, the
data do suggest that nitrate accumulation in winter greenhouse lettuce
may vary with the availability of nitrogen to the crop. Further
studies to identify a nitrogen fertility program that lowers nitrate
content of leafy vegetables without restricting crop production would
be worthwhile.

Another strategy for lowering nitrate concentration might be to
harvest crops on the afternoon of a sunny day, when the maximum amount
of nitrate assimilation has just occurred. In preliminary experiments
during winter at NAI, lettuce and other greens harvested late on a
sunny afternoon had 15 to 20 percent lower nitrate concentrations than
the same crops harvested early in the morning after a cloudy day.

Nitrate concentrations of lettuce from four of the greenhouses
exceeded the West German guideline maximum, whereas none exceeded the
maximum allowed in Austria and tho Nethorlands. In 1974, the World
Health Organization established an "acceptable daily intake" of 220 mg
nitrate for an adult,4 which might be consumed in a single large salad
containing two ounces of lettuce at 3,900 ppm nitrate. However, it is
difficult to compare the risk from winter greenhouse lettuce with that
of lettuce trucked in from California, which may be lower in nitrate
yet contain pesticide residues, and may have lost some nutrients in
transit. Researchers and growers should work together to identify
varieties and cultural practices that lower nitrate levels in winter
greenhouse vegetables. In the meantime, it may be advisable to eat
winter greenhouse-grown lettuce and other leafy vegetables in
moderation.

Mark Schonbeck

Mark is a research associate working on cover cropping and nitrogen in
vegetable production.

References
1. Lawrie Mott and Karen Snyder, 1988. Pesticide Alert. Organic
Gardening 35 (6): 70-78.
2. M. Schonbeck, 1987. "Nitrogen in the Composting Greenhouse." New
Alchemy Quarterly 29: 18-19.
3. C. Stopes, L. Woodward, G. Forde & H. Vogtmann, 1988. "The nitrate
content of vegetable and salad crops offered to the consumer as
from 'organic' or 'conventional' production systems." Biological
Agriculture and Horticulture 5 (3): 215-221.
4. H. Vogtmann 8c R. Biederman, 1985. The nitrate story: no end in
sight. Nutrition and Health 3: 217-239.
5. W.J. Corre & T. Breimer, 1979. Nitrate and Nitrite in Vegetables.
Center for Agricultural Publishing and Documentation, Wageningen,
Netherlands.
6. D. N. Maynard, A. V. Barker, P. L. Minotti Sc N. H. Peck, 1976.
Nitrate accumulation in vegetables. Advances in Agronomy 28:

[4]Web Site Index
__________________________________________________ _______________

Original Article from:
New Alchemy Quarterly
Fall 1988, No. 33
1988, New Alchemy Institute, Inc.
237 Hatchville Road
East Falmouth, MA 02536
[5]http://www.fuzzylu.com/greencenter/
Scanning & HTML conversion: FuzzyLu MultiMedia.

References

1. http://www.fuzzylu.com/greencenter/index.htm
2. http://www.fuzzylu.com/greencenter/q33/toc.htm
3. http://www.fuzzylu.com/greencenter/q33/parts/table1.gif
4. http://www.fuzzylu.com/greencenter/index.htm
5. http://www.fuzzylu.com/greencenter/home.htm












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Old 23-03-2003, 12:32 AM
 
Posts: n/a
Default Too much fertilizer makes vegetables poisonous?


if the first article didn't satisfy, then go to google and use the following
search terms and you will get approx 1900 more.....

+nitrate+vegetables+winter+accumulation



for the mustard arsenic issue....

+mustard+phytoremediation+arsenic


moral of the story....there are subtleties, even in gardening
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Old 23-03-2003, 02:44 AM
simy1
 
Posts: n/a
Default Too much fertilizer makes vegetables poisonous?

Tony wrote in message ...
I read somewhere that too much fertilizer can accumulate in leafy vegetables to
the point of being toxic for human consumption, does anyone know where I can
find out more about this, especially as it relates to hydroponics? I read this
in a book on green houses, it said something about problems with nitrogen not
being used up by the leafy vegetables in certain times of the year and thus
accumulating in the edible parts of the vegetable.

-Tony


It is true that some leafy greens, already a good source of proteins,
could get their nitrate levels so high as to irritate people with a
delicate digestive tract. That is why you don't want to give broccoli
to a baby younger than 1 year (ditto for chard). For most of us, it is
not a problem. One serving of broccoli has 5g of proteins and far far
less in the way of nitrates. Compare with a steak...
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Old 04-04-2003, 11:32 PM
mdk-bill
 
Posts: n/a
Default Too much fertilizer makes vegetables poisonous?

wrote:


if the first article didn't satisfy, then go to google and use the
following search terms and you will get approx 1900 more.....

+nitrate+vegetables+winter+accumulation

Lessee ... massive overfertilization, cold conditions and low light levels.

Nope ... none of those conditions prevail in my garden.

When people push N in an imbalanced manner in order to force poundage of
green veggies, they are not trying to grow _healthy_ veggies anyways; they
are trying to grow _lots_ of veggies without any but statutory regard for
the healthfulness of them. Plants need a lot of different nutrients, not
simply N, in order to produce the vitamins they are normally grown for.

According to my understanding, the standard NPK analysis for properly aged
compost is about 1-1-1. Thus, this is a problem that an organic gardener
would actually have to work very hard to have. It can't be done
accidentally in the normal home gardening situation.

What this research tried to establish is that it is possible to do stupid
things with plants. What it does NOT establish is that these stupid things
are likely to occur in a home setting.

I've read some of the other material published by the New Alchemy Institute
and, quite frankly, they remind me of chicken shakers dressed in beads,
feathers and paint. They have a mystical / political point to make and I
want nothing to do with it.

Their butterhead lettuce testing looked at a measly 42 heads. That sample
size is too small to be useful for anything except scaring the unwary.





for the mustard arsenic issue....

+mustard+phytoremediation+arsenic


This is a change in subject.

--
Do not respond to the email address above. It is a fake.

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Old 26-10-2003, 01:12 AM
Bill
 
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Default Too much fertilizer makes vegetables poisonous?

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?



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