Nitrate in leafy greens

[BenHehle Beamz]

Hi everyone,

has anyone tested the amount of Nitrate in Lettuce or other leafy greens yet?

Lettuce, (germany) measured : min. Conc.: 230mg/kg and max.Conc. 6810 mg/kg.

Regulation(germany): Summer and Wintersalad Nitrate conc. is not allowed to exceed 2500 and 3500 mg/kg. In Baby food the Nitrate conc. is now allowed to exceed 250 mg/kg.

If you harvest a lettuce at 6pm, it contains almost 50% less nitrate then a lettuce, harvested at 8 am.

Has anyone some ideas to decrease the concentration? Or what do you think about this topic, is it worth to "worry" about?

[TCLynx]

worrying about nitrate concentrations in plants has always kinda mystified me.  See leafy greens need a fair bit of nitrate to grow lush and fast but somewhere it seems that "nitrates" in one's food is bad?  Now I always took that to mean that things like nitrates used in meat preservation was not good to be consuming in large quantities but I never took that to mean that a person should avoid eating leafy greens.  I expect that nitrate levels in most of the healthier leafy greens than lettuce are probably higher so I don't get it?

I've also seen lists of plants that one should feed to chickens because of possibly toxic nitrate levels, now after keeping chickens for several years I realize that what the list really meant was if you feed your chickens exclusively on one of those plants with no other food available, the nitrate levels would be toxic.  I have not seen any of my chickens show toxic effects from eating any of the plants on that list since my chickens have free choice of many feeds available so a few cabbage, kale and sunflower leaves are not gonna hurt them.

[Jonathan Kadish NYC AA Chair]

I knew a little about this through my research i did about the nitrogen cycle. Plants are using the nitrates as building blocks for amino acids and many other organic molecules they use to grow. My interest was peaked again by your question and I found some good answers. A study was done and they found that nitrate deprived plants do indeed have a hard time producing amino acids, and in fact create more starches. Plants grown in a nitrate saturated solution have high levels of amino acids and organic acids. From what i found only some plants store nitrate and you would have to eat them like a cow - imaging eating 5 pounds of corn in 1 sitting... you can die by drinking to much water too [ http://jxb.oxfordjournals.org/content/56/410/309.full.pdf ]

Also,  " In the 1990s, a research group at Karolinska Institute demonstrated how the body can convert nitrate to NO, a molecule involved in many important bodily functions, such as blood pressure regulation, the immune defence and cell metabolism. These compounds can ameliorate mitochondrial dysfunction related diseases, The results, which are published in Cell Metabolism, are of sports-physiological interest, as they show that nitrate reduces oxygen consumption during physical exercise; however, they are also of potential significance to diseases involving mitochondrial dysfunction, such as diabetes and cardiovascular disease.,^[11]" - wiki

Thanks for the question, I know more now

[Alexandre Letellier]

Hi Ben, this bit got my attention :

 "If you harvest a lettuce at 6pm, it contains almost 50% less nitrate then a lettuce, harvested at 8 am."

Where did you get this info from ? I googled the sentence and the only relevant result was : " A number of nitrate tests were made in Oklahoma on forage sorghum cut from 8 a.m. to 6 p.m. The time of day did not affect the nitrate levels in the resulting hay." (http://missouribeginningfarming.blogspot.com/2011_07_01_archive.html )

I'd like to know more about this in the case of vegetables crops, thx...

[Alexandre Letellier]

A bit more google digging yielded this : Diurnal variation in the nitrate content of parsley foliage

It's a pretty technical academical paper but some parts of the discussion may apply to this thread : 

"Nitrate accumulation in plant tissues is particularly high during the winter when temperatures, light intensity and day length are less favorable for assimilation (Cantliffe 1972; Quinche, 1982; Fallovo et al., 2009; Chadjaa et al., 1999; Gaudreau et al., 1999; Blom-Zandstra, 1989). In previous studies, diurnal variations in the leaf nitrate concentration of spinach were reported depending on the genotype (Umar et al., 2007), but not in lettuce (Siomos, 2000). In parsley the lowering of foliar nitrate concentration at midday was observed in all three subspecies (Tables 2-4) irrespective of the cultivation season. It therefore appears that for parsley, harvest at midday offers a practical means of reducing nitrate concentration and thereby improving product quality. However, it is advisable that the leaves should be transferred immediately to a cool place or pre-cooled, since under conditions of high temperatures foliage may soon start to wilt after harvest if left exposed to the sun. Similar to lettuce (Demšar et al., 2004; Siomos et al., 2002), the older, outer leaves of parsley tend to accumulate nitrate more than the younger, inner leaves (Table 5). This may relate to the lower metabolic activity of the older leaves, which are then used by the plant as nitrate sinks. However, when harvest was carried out 2-3 weeks earlier than in the present experiments, the outer leaves still showed a higher concentration of nitrates than the inner leaves."

[BenHehle Beamz]

hi, i have to me more careful with my state, sorry. i got it from this website: http://www.bernd-leitenberger.de/nitrat.shtml Sorry, its in german. Here is what i found on: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1062103/?page=2

you can see the chart of No3 in spinache during the daytime, this ac. paper is very interesting.

Well, just in general it would be interesting to see the difference of no3 levels grown in AP compared to grown in soil or to hydroponics.

[Jonathan Kadish NYC AA Chair]

Sodium Nitrate is known to have toxicities that can be lethal, but you would have to eat about 20lbs of cured meat in one sitting to get that dose. We don't use that in aquaponics, and maybe there is a dose of nitates that would be lethal, but you would have to eat 100x more spinach than Popeye