Urea and ammonium

Just saw that one:

http://www.springerlink.com/content/h1v1108271270420/

It just confirms what I and quite a lot of others said, and the findings of most professional growers in the Netherlands... Orchids prefer urea, then ammonium, and eventually can cope with nitrate, but the latter is not their favorite.

Browse the AQ and the AOS bulletins from the early 80's, look at the plants, and you will see that many looked more happy with those urea fertilizes such as the old Peters and Plant-Prod than they are right now with those 'fantastic' nitrate-only fertilizers...

Useful info, thanks Sanderianum

I read that a couple of months ago. If anyone is a subscriber and can provide that entire article, I'd love to read it, as the abstract leaves a lot of questions. For example, I still don't see how they can reliably claim that "medium analysis revealed that no urea hydrolysis occurred before root absorption".

In the first place, mustn't it be hydrolyzed to be in solution in the first place? Secondly, even if they are intending to indicate that it is in the form of a hydrated urea molecule (and not NH4 or NO3) at the time it is absorbed by the velamen (which they did not state), that does not mean that the molecule isn't being further broken down into ammoniacal or nitrate forms before being taken up by the living root tissues. Don't forget that absorption by the velamen is not the same as use by the plant. It is actually more analogous to absorption by the medium, albeit a very fine and close medium, attached to the root tissues. And as plants balance ionic uptake with compensatory output, wouldn't the medium chemistry affect that, hence which ionic species is preferentially absorbed?

Another angle to consider is that ammoniacal, nitrate, and urea nitrogen sources all affect pH differently, both directly and from the plants' chemical reactions during assimilation. Under some conditions - particularly important is the alkalinity of the water and potting medium - the use of one over another might result in an improper pH level.

I'd also be curious of the chemistry of their growing media, as that can affect which form is taken up by the plant, as well. If you accept, at least for the moment, that urea must be broken down to ammonaical or nitrate forms in order to be assimilated by the plant (as opposed to being absorbed by the velamen), their medium chemistry will play a huge role in affecting the route the molecule follows.

...just too many questions to be able to make the unqualified statement that orchids like urea best.

Ray said:

...just too many questions to be able to make the unqualified statement that orchids like urea best.

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I agree that there are some mysteries in their research, but from the summary they provide, in a medium with nitrogen source composed of NH4+ NO3- and urea, they marked either NH4+ or NO3- or Urea using a radioactive isotope, and the nitrogen coming from the urea was taken first priority, then the nitrogen from the ammonium...

I have on my desk some Floricultura internal research, that they released only to a handful of cutomers in the early 90's. It shows clearly, using some dozen thousands plants of phalaenopsis clones, that 100% nitrate nutrition was the most troublesome, resulting in slower growth, more chlorotic leaves...

Right now on www.floricultura.nl they recommend the use of Peters or Plant Prod + calcium nitrate, and I know first hand that they are using Plant Prod preferably, which is a very high urea containing fertilizer. The Chineses and Taiwaneses phals grower use as well a very high urea fertilizer.

Anthura research ended up the same way, phals were best grown with urea in the feeding program. For me it is more than enough, and for sure far more than a couple of University studies, that are pale and tampered copies of the studies commended by those 2 large Dutch nurseries...

I found out actually that a fertilizer with ammonium and urea gives me constantly much nicer looking plants, and I no longer have the little chlorotic rim or slightly bleached color of the leaves that appeared with the all nitrate fertilizers.

Stupid question: Do Paph roots have a velamen at all? You guys talked a lot about Phals (highly appreciated), but can we assume that urea works equally fine with Paphs? Would it be taken up the same way?

labskaus said:

Stupid question: Do Paph roots have a velamen at all? You guys talked a lot about Phals (highly appreciated), but can we assume that urea works equally fine with Paphs? Would it be taken up the same way?

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Paphs roots definitely have velamen, but the thing I can say from experience, when I tried for a while the Excel and that kind of stuff with the NO3 nitrogen, I experienced serious plant quality problem. I tried a few times, and always the best solution has been for me the ammonium/nitrate/urea fertilizers.

I remember a discussion long time ago with Alan Moon from the Eric Young Fondation, and he told me that according to their experience - in rockwhool at that time - urea was absolutely essential to have a nice green foliage.

sanderianum,

Peters doesn't have any calcium or sulfur. Is the calcium nitrate added to Peters or just the PlantProd?

peters cal mag formulas have calcium nitrate added; if you have sulfur added as well to the concentrate barrel with calcium, you will have ice formation and a precipitation of the calcium and don't remember what else (what's that called, an endothermic reaction where heat is absorbed instead of given off, extremely chilling the solution). now, if you were able to mix the fertilizer in the final volume of water instead of a concentrate, you might get less precipitation but it would probably still lock up nutrients and minerals

also, a radioactive tracer test that shows that one type of fertilizer is taken up more quickly than another doesn't necessarily mean the plant prefers it more than another. it's fairly common horticultural knowledge that urea and ammonium fertilizers are taken up more quickly than nitrate types usually, in a wide range of plants. plants will look nicer with the hotter fertilizers because it will make more lush foliage. too lush foliage, though, can lead to more attacks of insects or diseases than tougher foliage. one of the big reasons why nitrate and cal mag fertilizers are quite popular in the horticulture industry is that the plants don't necessarily grow as fast as those with the first two types, meaning better controlled growth, hopefully shorter more compact plants that can fit on sales benches and shipping carts and trucks, so more can be fit on them. again it means trying to accommodate space and hope of less chemical applications to keep plants short (finances), rather than to have a very happy plant. so, the tests may not exactly prove that plants 'prefer' the hotter fertilizers, but I think in this case that they like 'food' that has more of them in it rather than the all nitrate ferts. I've started using different ferts on my plants rather than the plug feed I had been using all the time as the plants will definitely expand better if they have some sugar with the steak ; )

Here is the article! the pdf is big and i did it in pictures...!!!!!

Someone was nice enough to send me the article, and reading it thoroughly did give me a better feeling about their study, but did not do much to assuage my skepticism about their conclusions.

Charles is right - faster uptake does not imply "preference", and their data showed no significant statistical difference between urea and ammonia uptake.

We kust also keep in mind that they were working only with phals.

My experience is apparently different than sanderianum's - I have used Greencare Orchid Special (RO) exclusively for over 5 years. Its nitrogen is 12.5% nitrate and 0.7% ammonaical, and my plants are big, lush, and bloom like crazy.

For each paper that says urea is great, there are those that say it sucks. It is impossible for me to know what my plants want/need down to the milligram per liter. We use the buffet method... Many fertilizer formulas in organized random rotation. MSU formulas are the mainstay, but we use peters and friends with some correlation to bloom/grow seasons. Maybe if we found the Paphs like urea-free, but Parvis hate it, but the phals like urea, and the phrags only like it in January they would grow a little better, but I'm not about to have a different regime for each plant in the range. The scientist in me wants to know these things, don't get me wrong, but, shoot there are only so many hours in a day, and there are other cultural conditions that will have a more drastic impact on growth and flowering (light, proper watering, water chemistry, air...) IMO.

-Ernie

Ernie,

I'm with you. When you grow a mixed collection it is very difficult to zero in on one regimen that works best for everything.

I do stay away from urea (20-20-20) in the winter, because I believe that orchids simply can't break it down without higher temps and longer periods of daylight than we get. I'm in PA. According to Peters, it can actually hurt the orchids because they have to work too hard to break down the urea.

I would assume that the floricultura tests that showed urea to be beneficial were done for their growing conditions and thus were done at temps a lot higher than I can afford to provide (in the winter). (Sanderianum, these temps are probably normal year round for your area.) In addition, other articles by floricultura indicate their plants get a lot more light in the winter than I can provide (at a reasonable price).

Basic rule of thumb: Urea once per month during late spring, summer, and early fall. None otherwise.

Mike

orcoholic said:

Ernie,

I'm with you. When you grow a mixed collection it is very difficult to zero in on one regimen that works best for everything.

I do stay away from urea (20-20-20) in the winter, because I believe that orchids simply can't break it down without higher temps and longer periods of daylight than we get. I'm in PA. According to Peters, it can actually hurt the orchids because they have to work too hard to break down the urea.

I would assume that the floricultura tests that showed urea to be beneficial were done for their growing conditions and thus were done at temps a lot higher than I can afford to provide (in the winter). (Sanderianum, these temps are probably normal year round for your area.) In addition, other articles by floricultura indicate their plants get a lot more light in the winter than I can provide (at a reasonable price).

Basic rule of thumb: Urea once per month during late spring, summer, and early fall. None otherwise.

Mike

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I totally agree with what you say. Last spring I visited a major producer of very high quality Phalaenopsis in Holland. It uses only Peters Pro 20-20-20 with the addition of calcium nitrate. But we must not forget that its phalaenopsis are grown at a temperature of 28 °C. At this temperature ureases (an enzyme that converts urea to ammonia) are probably more active than at 20 ° C. This summer I tested on Dendrobium nobile a fertilizer containing its nitrogen as urea form. They were maintained during the day at a temperature of 30 ° C.The test was conducted during one month. After a fertilyser distribution on morning the effect of urea is visible at evening, the leaves take a beautiful dark green but I have not observed a faster growth. Anyway, as it is well known that the orchids (except perhaps the phalaenopsis) dislike a substrate which acidifies I continue to focus on fertilizer containing at least 80% of nitrogen as nitrate and balance as ammonia form , but without urea! Especially for paphiopedilums.

I think I'll try to pick the brains of Bill Argo (Tech Mgr @ Blackmore Co., and inventor of the MSU fertilizer formulas) and Paul Fisher (Prof @ Environmental Horticulture Dept and U of FL). They've been running a series of plant nutrition articles in Greenhouse Grower mag, and the latest installment, "Stock Plant Nutrition" (those you take cuttings from for propagation) has an unexplained comment that "Cutting quality tends to be better when the plants are grown with the majority of the nitrogen in nitrate form." On the assumption that there is some valid basis for that, I would guess they might be able to lend some further insight.

Back to the study's conclusion about preferential absorption of urea, I recall someone demonstrating the absorption capability of velamen by dipping orchid roots in water containing food coloring. Does that mean the plants "need" food coloring? As I recall, unlike many plants, feeding food coloring does not change living blossom colors, so I guess not.

Ray said:

I think I'll try to pick the brains of Bill Argo (Tech Mgr @ Blackmore Co., and inventor of the MSU fertilizer formulas) and Paul Fisher (Prof @ Environmental Horticulture Dept and U of FL). They've been running a series of plant nutrition articles in Greenhouse Grower mag, and the latest installment, "Stock Plant Nutrition" (those you take cuttings from for propagation) has an unexplained comment that "Cutting quality tends to be better when the plants are grown with the majority of the nitrogen in nitrate form." On the assumption that there is some valid basis for that, I would guess they might be able to lend some further insight.

Back to the study's conclusion about preferential absorption of urea, I recall someone demonstrating the absorption capability of velamen by dipping orchid roots in water containing food coloring. Does that mean the plants "need" food coloring? As I recall, unlike many plants, feeding food coloring does not change living blossom colors, so I guess not.

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No, the study is a bit clear on that, they checked the N type in the newest growing leaves, so it is not velamen absorption that they are talking about, but well a preference for urea, then ammonium, then nitrate in that order...

Bill Argo never invented the MSU fertilizers, they are just a copy of a public domain type of fertilizer called " Coic Lesaint" used since the 60's, just to be quite clear on that...