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 |
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. |
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 |
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 |
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 |
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 |
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... |
Too much fertilizer makes vegetables poisonous?
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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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