# Bleached leaves. Too much light or nutrition problem?



## papheteer (Mar 16, 2013)

Some of my plants have bleached leaves. Some look almost white with most mottling gone. Especially on my parvis. The new leaves come out darker and greener though. I have tried adding some magnesium sulphate in my water but not much changed. What do u guys think?

here are photos of my fanaticum's leaves:


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## eggshells (Mar 16, 2013)

What do you use for lighting? It looks like its not the lighting though. Because if it did. Top leaves will go change in colour first. I'm pretty sure that this is nutrient deficiency.


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## papheteer (Mar 16, 2013)

It used to be 12 inches under a 2 bulb t5hos. Then I moved it about 6 inches under 4 bulb 32watts t8s. Leaves still bleached.


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## SlipperFan (Mar 17, 2013)

Need nitrogen? Or magnesium?


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## lepetitmartien (Mar 17, 2013)

No unwanted cold exposure?

How are roots?

(just covering all areas… sorry if dumb, I'm too sexy for my shirt


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## papheteer (Mar 17, 2013)

No cold exposure. I grow them in the basement. It's recently repotted. Lots of roots.


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## mrhappyrotter (Mar 17, 2013)

I'll defer to the experts, which I definitely do not claim to be. That being said, the photos do look awfully suspicious.

What's your fertilizing regime like in terms of type(s) of fertilizer used, how often and how much?

I don't have a lot of knowledge about nutrient deficiency in orchids -- mostly because I've not had much experience with it. However, in other plants, yellowing older leaves like that is a sign of nitrogen deficiency.

That doesn't necessarily mean that you aren't giving your plant sufficient amounts of nitrogen (or whatever nutrient). It could mean that the nitrogen source isn't readily available to the plant, for instance if the pH isn't correct for the form of nitrogen you're providing or because other nutrients are blocking it's uptake (i.e. nutrient imbalance).

Also, if the plants are under higher light conditions and therefore growing rapidly (or trying to grow rapidly), it could exasperate the situation.

Anyway, I'm sure someone more knowledgeable will chime in on this.


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## papheteer (Mar 17, 2013)

I have been using k-lite at 1/10 -1/8 tsp per gallon of water. I also supplemented with crushed oyster shells. The one that i got was very powdery. I did notice that after putting it all the root tips stopped growing. I dunno if its coz of that.


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## mrhappyrotter (Mar 17, 2013)

I've also been told, and read, that bark based mixes require higher nitrogen feeding rates than plants in other media. Not sure if this has been proven or debunked, but the reasoning is that the microorganisms that live on/in the bark and break it down consume a lot of nitrogen in the process, and can out compete plants in its uptake.


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## Stone (Mar 17, 2013)

Yes more N. and I would recommend Ammonium or Urea added to your normal fertilizer. Or even better a slow release form like IBDU. Don't expect fast results. 3 months or more I would say. Its absolutely a fact the bacteria consume a lot of N and can totally starve a plant if not enough is added. Every organic ingredient has a different Nitrogen draw-down with peat very low and uncomposted bark very high.
Try to increase the N by 50 to 100% and see how the plant responds.


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## Cochlopetalum (Mar 17, 2013)

papheteer said:


> I have been using k-lite at 1/10 -1/8 tsp per gallon of water. I also supplemented with crushed oyster shells. The one that i got was very powdery. I did notice that after putting it all the root tips stopped growing. I dunno if its coz of that.



I think your plants are a bit close to the light still and you are feeding at very a low rate. I would feed them a stronger solution around 1/3 tsp per gallon and rais the lights a bit more.


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## paphreek (Mar 17, 2013)

Another point to consider is when you are taking such a tiny sample (1/8 tsp.) of the fertilizer and mixing it up, it may not be balanced with the right proportions of nutrients. I recommend taking a larger amount, according to directions, and making a liquid concentrate. The concentrate should be closer to the formula of the fertilizer than a 1/8 tsp. scoop. Once you have the concentrate, feed at 75-100 ppm of N.

Also, what kind of water are you using?


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## keithrs (Mar 17, 2013)

Possibly iron?


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## Ray (Mar 17, 2013)

I think you have done a number of things that are combining to cause the issue:

►Powders can certainly negatively affect roots, often by desiccating them. 

►Excessive calcium can interfere with magnesium uptake. Powders have a lot of surface area, after all, so maybe the oyster shell powder is interfering chemically, as well as physically.

►You are underfeeding. The K-Lite formula at 1/8 tsp/gal is only supplying about 20 ppm N. That might be sufficient for daily feeding, but not likely so for a less-frequent regimen.

on other comments:

►If you leave a plant in the same bark for a very long time, as it breaks down there will ultimately become a hefty population of lignin-consuming microorganisms that consume nitrogen. Modern, attentive culture, and better quality barks pretty much preclude that.

►I think Stone's suggestion is a good "quick fix", but if you supplement with urea, use it as a foliar spray, and it's not as well absorbed through the roots.


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## papheteer (Mar 17, 2013)

Thanks guys!


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## papheteer (Mar 17, 2013)

Ray said:


> I think you have done a number of things that are combining to cause the issue:
> 
> ►Powders can certainly negatively affect roots, often by desiccating them.
> 
> ...



Ray i feed almost every time i water. I use RO with 20% tap water added. My tap water has TDS of 180. 

I will try and feed more. Should i use 1/3 tsp per gallon everytime i water?


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## papheteer (Mar 17, 2013)

paphreek said:


> Another point to consider is when you are taking such a tiny sample (1/8 tsp.) of the fertilizer and mixing it up, it may not be balanced with the right proportions of nutrients. I recommend taking a larger amount, according to directions, and making a liquid concentrate. The concentrate should be closer to the formula of the fertilizer than a 1/8 tsp. scoop. Once you have the concentrate, feed at 75-100 ppm of N.
> 
> Also, what kind of water are you using?



I always make a solution of 2 tsp to 500 ml water and take from it.


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## Rick (Mar 17, 2013)

papheteer said:


> I have been using k-lite at 1/10 -1/8 tsp per gallon of water. I also supplemented with crushed oyster shells. The one that i got was very powdery. I did notice that after putting it all the root tips stopped growing. I dunno if its coz of that.



If you are using K lite (especially at a weak rate like 1/10 tsp per gal) and add high carbonate potting amendments (like oyster shell) then you are setting yourself up for nitrogen deficiencies. 

K lite nitrogen is nitrate based which is most efficiently used by plants in low alkalinity (low carbonate/bicarbonate) systems. As you increase the root zone alkalinity plants would like to see more ammonia (as from urea). 

What is the alkalinity of your irrigation water? Are you using RO or rain water? If you use tap water, that could already supply enough bicarbonate to require ammonia/urea before the addition of calcareous pot amendments.


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## Rick (Mar 17, 2013)

Ray said:


> I think you have done a number of things that are combining to cause the issue:
> 
> 
> ►Excessive calcium can interfere with magnesium uptake. Powders have a lot of surface area, after all, so maybe the oyster shell powder is interfering chemically, as well as physically.
> ...



Both of the above are good points. Calcium/magnesium balance, and oyster shell is a phosphate absorber too. Not to mention all the alkalinity problems introduced with oyster shell and your tap water. By adding the oyster shell you essentially negate the dilution of your tap water. 

You can feed K lite at low doses as you describe on a daily basis, and it would work well, but you need to start out with more dilute irrigation water and no calcareous pot amendments.


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## Silvan (Mar 17, 2013)

I was just wondering what was the temperature in your growing area ?
I grow my parvis outside for the summer and around october when the temperature shifts, if I wait too long to bring them inside they shed some leaves... maybe if your plants were expose to a draft or cooler temperature that would have cause some leaves to yellow..


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## papheteer (Mar 17, 2013)

Silvan my plants are never exposed to drafts or cold temperatures. Min temp is around 55f and max is 80. But usually its between 60-75f.


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## papheteer (Mar 19, 2013)

What do you guys suggest I do with plants that have oyster shell top dressing? Some of them are recently repotted so repotting again to get rid of the shells is not really an option. Should I just use more K-lite (1/3 tsp per gallon) in PURE RO water? Should I try using a different fertilizer with more ammoniacal/urea nitrogen? Thanks!


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## papheteer (Mar 19, 2013)

Also, after adding more nitrogen, roughly how long does one have to wait to see some improvements?


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## Rick (Mar 19, 2013)

papheteer said:


> What do you guys suggest I do with plants that have oyster shell top dressing? Some of them are recently repotted so repotting again to get rid of the shells is not really an option. Should I just use more K-lite (1/3 tsp per gallon) in PURE RO water? Should I try using a different fertilizer with more ammoniacal/urea nitrogen? Thanks!



I know your basic garden center should carry ammonium sulfate. You could probably add a pinch of that.


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## Rick (Mar 19, 2013)

papheteer said:


> Also, after adding more nitrogen, roughly how long does one have to wait to see some improvements?




some people on this site have seen measurable improvements after a week after N and Mg spiking.


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## andre (Mar 19, 2013)

I have had some uneven leaf colour on my Paphs. from using pesticide and or RD20 at too high concentrations... The strap leafed ones get blotchy, and the mottled leafs get a bit light. Does not look like your plants, but it's something that I have done a couple of times... 

On that note... No access to K-lite, but living in Vancouver there is an astronomical number of hydroponic shops, there is a product called cal-mag, and any ratio of NPK you can think of. I might have a go at mixing a fert. I do have a PH and TDS meter.... Hmmm. 

Also anyone have any tips on ratio mixing RD20, Bayer Rose systemic, and captain? Not that I have a huge problem... Mostly to spray new plants ect. I grow under lights 8X4foot T5 reflector unit.


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## papheteer (Mar 19, 2013)

Thanks, Rick. If i find some ammonium sulfate, how much should I add to my water?


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## Rick (Mar 19, 2013)

Since you are in Canada there is something that could be vastly superior to ammonium sulfate.

The product is ammonium magnesium phosphate. Or magnesium ammonium phosphate (heptahydrate)

It is produced/patented by a company called Ostera in Vancouver.

Some times this is called magamp, but it is actually a biologically formed mineral called struvite (a type of kydney stone).

Ostera patented the product under "Crystal Green"

It can actually made from urine, and in the US I see kits for sale to "make your own" from your own urine:drool:

At this point I have not been able to find a US distributor of straight struvite, but Jack's fertilizer has it added to one of their products (High K though).


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## Paphman910 (Mar 19, 2013)

Stone said:


> Yes more N. and I would recommend Ammonium or Urea added to your normal fertilizer. Or even better a slow release form like IBDU. Don't expect fast results. 3 months or more I would say. Its absolutely a fact the bacteria consume a lot of N and can totally starve a plant if not enough is added. Every organic ingredient has a different Nitrogen draw-down with peat very low and uncomposted bark very high.
> Try to increase the N by 50 to 100% and see how the plant responds.



I agree with his statement! I have been using a high nitrogen fert 25-10-10 with nutricote that is 20-7-9


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## papheteer (Mar 19, 2013)

Paphman are you using the plant prod Orchid fertilizer? Eggshells suggested i use that one. Fingers crossed my plants green up soon!


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## Paphman910 (Mar 19, 2013)

papheteer said:


> Paphman are you using the plant prod Orchid fertilizer? Eggshells suggested i use that one. Fingers crossed my plants green up soon!



Yes it is Plant Prod. Hope it works out for you. Just make sure you check your pH of the water coming out of the pot after watering.


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## Eric Muehlbauer (Mar 19, 2013)

An astronomical number of hydroponic shops in Vancouver, BC! Wow! I wonder why......................................


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## Rick (Mar 19, 2013)

Paphman910 said:


> Just make sure you check your pH of the water coming out of the pot after watering.



What do you want the pH to be and which way do you expect it to go? Also what is the remedy for an incorrect pH?

Are you using pH as a proxy for alkalinity? 

I see the potential for the snowball effect. More ammonia = dropping pH = more lime (alkalinity needed) = more ammonia needed = dropping pH = ........

Until pot TDS is through the roof and the roots are burned off.

As Stone mentioned, the amount of N utilized by soil bacteria (actually the same nitrifiers that handle the ammonia waste of fish in your basic aquarium system) can be substantial. But the more you feed the more you get. And they suck up alkalinity in the process (thereby lowering pot pH and promoting that viscous cycle). 

So you can keep the alkalinity low to start with (get rid of alkaline pot supplements), feed a small amount of a high nitrate percentage feed source (that the nitrifying bacteria cannot use), and break out of the cycle of overfeeding/flushing/media breakdown....

It really is like an aquarium. Feed the fish and not the bacteria in the filter. Keeps the water quality up with less maintenance.


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## Bjorn (Mar 20, 2013)

Rick said:


> What do you want the pH to be and which way do you expect it to go? Also what is the remedy for an incorrect pH?
> 
> Are you using pH as a proxy for alkalinity?
> 
> ...



This interests me:drool: How can I in a relatively precice way determine pH of the "root-water"? With very diluted fertilizers (TDS 100ppm) and very open mixes, how do we measure it? I have tried pH meters and indicators, but frankly, this is not straight forward.
Another thing is an obesrevation I have made with fertilizer solutions containing urea. Let me explain; 
Ok immediately after mixing, the pH is, say 5.1 at a conductivity of 160 microsiemens/cm (uncertain about the units, correct me if I am wrong) with quite a bit of urea this should be close to a TDS of 100ppm. If the same water is poured into a cup and kept for a day or two, the pH can be measured to 7.0 and conductivity to 190 microsiemens/cm. Here its imaginable that the urea splits to ammonia causing this change. So far so good?
Here comes the question: if the water changes during storage(hours!) how is the situation down at the root level? Would not ammonia (NH3) consume H+ and increase the pH of the mix? Ok, if it is absorbed by the plant, locally H+ is released and this can lower the pH locally. However, if you water every day or so (like I do), at every watering, the root system get flushed with fresh fertilizer and I would claim that there is no chance of a quantitative conversion of the urea to make the mix become acid. Chances are that the opposite happens, that the urea causes the substrate pH to increase instead.
Then my final question: for very open mixes with fairly low CEC; how do I measure the pH? Has anyone actually conducted this exercise?


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## limuhead (Mar 20, 2013)

Could it be potassium deficiency?


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## DavidCampen (Mar 20, 2013)

Bjorn said:


> Here comes the question: if the water changes during storage(hours!) how is the situation down at the root level? Would not ammonia (NH3) consume H+ and increase the pH of the mix? Ok, if it is absorbed by the plant, locally H+ is released and this can lower the pH locally. However, if you water every day or so (like I do), at every watering, the root system get flushed with fresh fertilizer and I would claim that there is no chance of a quantitative conversion of the urea to make the mix become acid. Chances are that the opposite happens, that the urea causes the substrate pH to increase instead.


That is my opinion. Also don't forget another argument seen here, that I disagree with, about ammonia requiring alkalinity because conversion of ammonia to nitrate by bacteria produces H+; if so then again the pH increase from the urea converting to ammonia would be offset by the acid produced when the ammonia is converted to nitrate. But, actually, there is yet even another balancing processes - OH- is released when nitrate is taken up by the plant and this counters any H+ produced when ammonia was converted to nitrate. All of these factors plus the other important one you mention, flushing with new water nutrient solution every day or so, make these concerns about urea and ammonia to be not very significant. When you a preparing a field for planting corn then you have to be concerned with the acidifying and alkalizing effects of your fertilizer, as Bill Argo does in a paper cited on this forum, but not hardly with orchids that are very frequently flushed with new nutrient solution.


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## The Mutant (Mar 20, 2013)

I have the same problems... I'll see if I can get my hands on some ammonium sulfate. 

*EDIT:*

I just realized that most of my Paphs with pale, yellowing leaves, are Paphs that I haven't repotted... They're still in the same substrate as when I got them. Maybe that has got something to do with it. I'll repot the worst cases (such as my lowii) and see how they react.

Thanks for a good thread!


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## Ray (Mar 20, 2013)

Bjorn said:


> Then my final question: for very open mixes with fairly low CEC; how do I measure the pH? Has anyone actually conducted this exercise?



I agree with David on this one. In such low-CEC/frequent irrigation circumstances, the root environment is pretty much that of the as-applied solution. Sure, there is some modification by the plants themselves, but I believe it is overwhelmed by the solutions' properties.


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## Rick (Mar 20, 2013)

limuhead said:


> Could it be potassium deficiency?



Typical symptoms of K deficiency are leaves becoming yellow and then necrotic (like burnt) at the ends of the leaves. These are yellowing from the bases of the leaves.

K deficiency is unlikely (unless caused by antagonism of too much of something else). But in the general scheme of things excess K causes deficiencies of a wide range of nutrients rather than the other way.


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## Rick (Mar 20, 2013)

DavidCampen said:


> because conversion of ammonia to nitrate by bacteria produces H+; But, actually, there is yet even another balancing processes - OH- is released when nitrate is taken up by the plant and this counters any H+ produced when ammonia was converted to nitrate.



You are assuming that an equal amount of N is being consumed by both the nitrifiers and the plants in this balancing act.

But in reality you can build a bacterial population that can handle way more ammonia than the plant is able to uptake NO3. So net balance you end up with alkalinity loss and acidification.

Pot pH drop is a studied phenomena. Several years ago Orchids published a study that was designed to look at the percieved need of calcium for paphs. Using basic bark based potting mix different levels of lime amendment, and a standardized watering a feeding regime (some basic 20-20 -20 I believe) they were able to get pot pH to drop below 4 in unamended pots in less than a year (if I remember correctly). While ammended pots dropped more slowly.

That article has been referenced on this site but 3-5 years ago.


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## Rick (Mar 20, 2013)

Bjorn said:


> This interests me:drool: How can I in a relatively precice way determine pH of the "root-water"? With very diluted fertilizers (TDS 100ppm) and very open mixes, how do we measure it? I have tried pH meters and indicators, but frankly, this is not straight forward.
> Another thing is an obesrevation I have made with fertilizer solutions containing urea. Let me explain;
> Ok immediately after mixing, the pH is, say 5.1 at a conductivity of 160 microsiemens/cm (uncertain about the units, correct me if I am wrong) with quite a bit of urea this should be close to a TDS of 100ppm. If the same water is poured into a cup and kept for a day or two, the pH can be measured to 7.0 and conductivity to 190 microsiemens/cm. Here its imaginable that the urea splits to ammonia causing this change. So far so good?
> Here comes the question: if the water changes during storage(hours!) how is the situation down at the root level? Would not ammonia (NH3) consume H+ and increase the pH of the mix? Ok, if it is absorbed by the plant, locally H+ is released and this can lower the pH locally. However, if you water every day or so (like I do), at every watering, the root system get flushed with fresh fertilizer and I would claim that there is no chance of a quantitative conversion of the urea to make the mix become acid. Chances are that the opposite happens, that the urea causes the substrate pH to increase instead.
> ...



Most of us aren't watering every day. So I would agree if you water that freqently and have a low water retentive and low CEC mix, then pH in is probably close to pH out. But it sounds like many only water once or twice a week, and use water absorbant mixes. So in that case plug the pot and fill with RO water. Give it an hour or so and then test. Or pour through a pot several times until you get an equilibrium value.


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## Rick (Mar 20, 2013)

Bjorn said:


> Would not ammonia (NH3) consume H+ and increase the pH of the mix? :



Only if your mix is sterile.

But the nitrifying bacteria are very good at colonizing mixes and they "eat ammonia" and drop pH as they do so.

Basic waste water, and aquarium technology.


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## DavidCampen (Mar 20, 2013)

Rick said:


> You are assuming that an equal amount of N is being consumed by both the nitrifiers and the plants in this balancing act.
> 
> But in reality you can build a bacterial population that can handle way more ammonia than the plant is able to uptake NO3. So net balance you end up with alkalinity loss and acidification.


And you are assuming that most or all of the nitrogen is coming from ammonia. 



> Pot pH drop is a studied phenomena. Several years ago Orchids published a study that was designed to look at the percieved need of calcium for paphs. Using basic bark based potting mix different levels of lime amendment, and a standardized watering a feeding regime (some basic 20-20 -20 I believe) they were able to get pot pH to drop below 4 in unamended pots in less than a year (if I remember correctly). While ammended pots dropped more slowly.


What does this have to do with the use of ammonia as a nutrient? Was the change in pot pH correlated to the use of ammonia?


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## DavidCampen (Mar 20, 2013)

Rick said:


> Most of us aren't watering every day. So I would agree if you water that freqently and have a low water retentive and low CEC mix, then pH in is probably close to pH out. But it sounds like many only water once or twice a week, and use water absorbant mixes. So in that case plug the pot and fill with RO water. Give it an hour or so and then test. Or pour through a pot several times until you get an equilibrium value.


If so this is then a good argument for watering frequently, not for worrying about a portion of the nitrogen in your fertilizer coming from ammonium.


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## Rick (Mar 20, 2013)

http://www.thewaterplanetcompany.com/docs/WPC_Nitrification & Denitrification .pdf

As it turns out there is a 7-1 alkalinity to ammonia consumption rate by nitrifciation.

So if you supply ammonia to a biologicially active substrate with nitrifiers, it will definitely acidify your mix at a very high rate.


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## DavidCampen (Mar 20, 2013)

Rick said:


> http://www.thewaterplanetcompany.com/docs/WPC_Nitrification & Denitrification .pdf
> 
> As it turns out there is a 7-1 alkalinity to ammonia consumption rate by nitrifciation.


What is said is that 1 pound of ammonia when converted to nitrate produces enough acid to react with 7 pounds of calcium carbonate. So what? 

The nitrate produced from 1 pound of ammonia, when taken up by a plant releases alkalinity equivalent to 3.5 pounds of calcium carbonate and the uptake of the anion that accompanied the ammonia produces the other 3.5 pounds of calcium carbonate equivalent.



> So if you supply ammonia to a biologicially active substrate with nitrifiers, it will definitely acidify your mix at a very high rate.


Yes, if you fertilize with pure ammonium sulfate and don't flush your pot.


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## Rick (Mar 20, 2013)

DavidCampen said:


> What is said is that 1 pound of ammonia when converted to nitrate produces enough acid to react with 7 pounds of calcium carbonate. So what?
> 
> The nitrate produced from 1 pound of ammonia, when taken up by a plant releases alkalinity equivalent to 3.5 pounds of calcium carbonate and the uptake of the anion that accompanied the ammonia produces the other 3.5 pounds of calcium carbonate equivalent.



However the plant uptake rate is a fraction of the nitrification rate.

A full Cattleya leaf ways less than 1 gram dry and only contains 3% N (30 mg total). And it takes several months of (weekly?) fertilizer applications to get there. So the alkalinity addition by plants is insignificant compared to the alkalinity uptake rate of the potting mix bacteria.

And then regular heterotrophs are doing their magic and releasing CO2 from general respiration (going to carbolic acid and further reducing pH).

Biology happens, and a little bacteria can do a lot.


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## DavidCampen (Mar 20, 2013)

Rick said:


> However the plant uptake rate is a fraction of the nitrification rate.
> 
> A full Cattleya leaf ways less than 1 gram dry and only contains 3% N (30 mg total). And it takes several months of (weekly?) fertilizer applications to get there. So the alkalinity addition by plants is insignificant compared to the alkalinity uptake rate of the potting mix bacteria.
> 
> ...



Most all of the nitrate that plants take up in nature comes from conversion of the nitrogen in dead plants etc. to ammonia and thence to nitrate. It is amazing that the plants manage to survive in nature without our strenuous intervention.


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## Rick (Mar 20, 2013)

DavidCampen said:


> Most all of the nitrate that plants take up in nature comes from conversion of the nitrogen in dead plants etc. to ammonia and thence to nitrate. It is amazing that the plants manage to survive in nature without our strenuous intervention.



http://elmu.umm.ac.id/file.php/1/ju...rimental Botany/Vol44.Issue3.Nov2000/1236.pdf

Yup orchid growers are generally in overkill mode.

The attached paper doesn't want to open fully for me, but a table near the end shows solution (looks like a hydroponic test) pH drop with use of NO3, NH3, glutamine, and various combinations thereof for nitrogen sources.

The biggest drops from the initial pH are for high percentage ammonia solutions.


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## DavidCampen (Mar 20, 2013)

Rick said:


> http://elmu.umm.ac.id/file.php/1/ju...rimental Botany/Vol44.Issue3.Nov2000/1236.pdf
> 
> Yup orchid growers are generally in overkill mode.
> 
> ...



The paper also notes:
_*Our results suggest that organic N and NH4 ions are the main sources of nitrogen to C. fimbriatum. Some of the physiological characteristics detected in C. fimbriatum plants are typical of plant species adapted to tropical and subtropical rainforest climax communities* (Stewart et al., 1992) and of plants species adapted to extreme soil conditions (Claussen and Lenz, 1999; Schmidt and Stewart 1999). Beyond representing an interesting model plant or physiological studies, the genus Catasetum comprises several species of economic value. Our results pointed out the advantageous use of glutamine for a more efficient development of Catasetum plants. *It was also evident that NO3 alone is a poor nitrogen source for Catasetum growth.*_


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## Rick (Mar 20, 2013)

Yes. But neither did it say that NO3 was totally useless either. 


I also wouldn't be surprised given that they started at pH of 5.5 and let it go down from there. 

Everything else (like K, Mg, PO4) concerning sugar/energy production (the primary criteria by which they assessed N choice) gets hard for the plants to access at those low pH values. So what would the results be like like with pH support in the typical 5.5-6.5 range considered optimal for orchids.

The best material was actually the glutamine (not ammonia), and from the what I picked up they felt organo-nitrogen sources were the best (for Catasetum fimbriatum). This also may not be that surprising since many Catestum are tended by ants that add all kinds of to the piles of shredded leaves they add around plants like this.

How much soluble carbon support do we give our plants? Of the dry matter in plants about 90% if it is in carbon based products. So plants need carbon much more than NPK......

The chelators you like to use may be a good source.

I use kelp.


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## consettbay2003 (Mar 20, 2013)

Rick, I recall that you use 1/4 tsp. of kelp/gallon of water once a week when you fertilize. Would there be any downside or upside in increasing this to 1/2 tsp/gallon once a week?


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## Rick (Mar 20, 2013)

http://aob.oxfordjournals.org/content/early/2012/07/08/aob.mcs140.abstract

This is a very interesting abstract on ant plants, but doesn't include anything to the discusion of nitrate (maybe urea though).


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## Rick (Mar 20, 2013)

consettbay2003 said:


> Rick, I recall that you use 1/4 tsp. of kelp/gallon of water once a week when you fertilize. Would there be any downside or upside in increasing this to 1/2 tsp/gallon once a week?



Probably not, but the long term concern is hormonal overdose. Ray might have more to say on kelp dose, but I think even 1/2 tsp/gal is way below the suggested weekly dose suggested for food crops.

You might consider focusing increased dosing of anything on warm/bright times and big plants. Winter and small plants hold off.


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## Ruth (Mar 20, 2013)

Very interesting discussion



> I know your basic garden center should carry ammonium sulfate. You could probably add a pinch of that.


If you use it as a folar spray, how much would you use to a gallon of water


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## Stone (Mar 20, 2013)

Here are a few points on what happens in pots regarding pH and fertilizers. 

Repeated application of fertilizers which contain higher Ammonium and Urea than nitrate will acidify media over time so sooner or later lime must be applied if you want to avoid damaging your plants with a very acid mix.

This is a list of the Calcium carbonate needed to restore pH after using certain fertilizers: Kg per Kg........
Ammonium sulphate: 1.1
Urea: 0.75
Ammonium nitrate: 0.6
Ammonium phosphate 0.5
Dried blood: 0.2

If a fertilizer contains equal amounts of NH4 and NO3 should not alter pH wheather or not the NO4 is converted to nitrate before use by the plant because bicarbonate ions released by the roots as they take up NO3 will balance the acidity produced when ammonium is taken up or converted to nitrate.
BUT!!..... It is usually found in nurseries that pH drifts down anyway because of leaching of nitrate produced from ammonium. Not that lost from fertilizer NO3.
It is believed that acidification is due more to this than the direct effect of ammonium. So ferts with a 2 or 3 to 1 NO3 to NH4 ratio should prevent acidification.

Calcium nitrate will make a media more alkaline but the effect is small. 0.2kg of sulphur will neutralize 1 kg of Calnitrate.


So in theory you should be able to juggle your fertilizer components to sabilize your mix pH without resorting to lime but in practice I think its wize to keep tabs on mix pH with 6 monthly checks and use some lime if needed.

It seems that many orchids are happy with (or prefer) ammonium so I think the 2 to 1 nitrate to ammonium is probably a good ratio. Although most of my orchids are fed with 95% urea and ammonium N in a controlled release form and most are thriving! But I do sprinkle 50/50 dolomite/limestone on the pots once or twice a year.


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## Stone (Mar 20, 2013)

Rick said:


> > How much soluble carbon support do we give our plants? Of the dry matter in plants about 90% if it is in carbon based products. So plants need carbon much more than NPK......
> 
> 
> 
> What do you mean by carbon support? Don't they get the carbon from air?


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## Stone (Mar 20, 2013)

Bjorn said:


> > Then my final question: for very open mixes with fairly low CEC; how do I measure the pH? Has anyone actually conducted this exercise?
> > [/
> 
> 
> ...


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## Rick (Mar 20, 2013)

Stone said:


> Here are a few points on what happens in pots regarding pH and fertilizers.
> 
> If a fertilizer contains equal amounts of NH4 and NO3 should not alter pH wheather or not the NO4 is converted to nitrate before use by the plant because bicarbonate ions released by the roots as they take up NO3 will balance the acidity produced when ammonium is taken up or converted to nitrate.


Noting that pH drop is observed even when balance of ammonia and nitrate is present is covered in that one pdf I posted. The bacterial acidification caused by nitrification of ammonia is disproportionate to the amount of alkalinity gained by the tiny amount the plant releases via nitrate uptake. You brought up what I think is a very important point in that bacteria are able to remove/convert considerable amounts of ammonia (mostly to nitrate anyway). And they are competing with the plant for that same ammonia.

But a plant in a pot is always going to loose the arms race to an active and growing bacteria population. As long as you keep shoveling in ammonia, and adding alkalinity the bacteria multiply at rates plants (or plant growers) can only dream about. Nitrifiers operate 24/7, and respond over temperature ranges better than the plants. Plant activity is focused on daylight activities.

The option of running higher nitrate/ammonia ratios and operating at lower alkalinity starves the bacteria population, and keeps it from predominating pot conditions. A periodic "shock" of ammonia has a greater chance of actually getting into a plant, when it doesn't have to compete with the nitrifiers.


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## Rick (Mar 20, 2013)

Stone said:


> Rick said:
> 
> 
> > What do you mean by carbon support? Don't they get the carbon from air?
> ...


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## Rick (Mar 20, 2013)

Actually lots of amino acid in kelp extract and glutamic acid is about the highest abundance of all of them.


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## Rick (Mar 20, 2013)

http://www.google.com/patents/EP2229054A1?cl=en

Crazy

Check out this patent for use of amino acids as plant/mycorrhizae fertilizer!!


All these amino acids are in kelp, so don't know how you can patent this.


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## Stone (Mar 21, 2013)

Rick said:


> > But a plant in a pot is always going to loose the arms race to an active and growing bacteria population. As long as you keep shoveling in ammonia, and adding alkalinity the bacteria multiply at rates plants (or plant growers) can only dream about. Nitrifiers operate 24/7, and respond over temperature ranges better than the plants. Plant activity is focused on daylight activities
> 
> 
> .
> ...


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## Dido (Mar 21, 2013)

Rick said:


> http://www.google.com/patents/EP2229054A1?cl=en
> 
> Crazy
> 
> ...



I think this is specific patent for the use of exactly content of pure aminoa acids. 
The content in kelp is extremly viable depending on which lep you use and where it has grwon year .....
It is like a good wine. Here they use mostly extracted amino acids, it is the same that soem companys use amino acid for chelating trace elements for better bio availability. You can make a patent on nealy everything if you can pay the cost, show that you are the first one who did it and register it, its not only the ingredient it is the idea or maybe the use you can make a patent on.


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## Ray (Mar 21, 2013)

I know this is unrelated, but these last few posts about bacteria reminded me of something interesting:

Think oils spills and "oil eating super-bugs". The technology works, but the "bug" population fades away quickly, so they need to be replenished. Having worked in the petrochemical and refining industry for 30 years, I learned that in the Exxon Valdiz spill, Elf Aquitaine (my company) utilized an updated method that was far more effective: spray an emulsion of olive oil and high-nitrogen fertilizer on the spill. The N sparks an explosion in the population of indigenous bacteria, who start by consuming the light, and easy to devour olive oil. As the population expands and the olive oil supply dwindles, they go after the heavier oil! This will work on your driveway too, but don't slip on the olive oil.

So do we know of K-eating bacteria we can seed the potting media with to clean it up?


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## gonewild (Mar 21, 2013)

Ray said:


> As the population expands and the olive oil supply dwindles, they go after the heavier oil! This will work on your driveway too, but don't slip on the olive oil.



Not recommended for asphalt driveways. And hope the bacteria does not climb your tires and go after your engine. 
:wink:


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## Bjorn (Mar 21, 2013)

Rick said:


> Only if your mix is sterile.
> 
> But the nitrifying bacteria are very good at colonizing mixes and they "eat ammonia" and drop pH as they do so.
> 
> Basic waste water, and aquarium technology.



Guess its ammonia they eat  you have a point, provided your bacterial(nitrosomonas) population is high enough to oxidize enough of the ammonia. Guess the net reaction going from NH3 to NO3- is one H+ in excess? But if your pH is 5.5 or so then your nitrosomonas would not be very active or?  And of course enough Nitrobacter has to be present as well since we are not interested in nitrite that is the product of the nitrosomonas. Nitrobacter enjoy pH levels of slightly above 7 so perhaps they do not like the acid bark after all? 
Btw. I do water frequently, but drawing a comparison to aquariums is perhaps to exaggerate a bit oke:
Joke aside;
Another thing is the fact that those of you that uses well water should pay a bit attention to the alkalinity, or carbonate hardness as its called over here. It is capable of altering the pH balance of your mix more that the possible urea will. At my place I have water from a well that gives an alkalinity of 250ppm. Fresh the pH is around 7 but that is due to dissolved CO2. after a while it attains values of 8-8.5. If I would use that for irrigation, it would totally dominate the pH given my fertiliser addition is at only some 200ppm. I try to control the pH of my irrigation water to be slightly below 6. That is easy by using rainwater, but with the well water I would probably run into trouble; as I did with my fresh-water aquarium. Its ok now


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## eggshells (Mar 21, 2013)

Bjorn said:


> Another thing is the fact that those of you that uses well water should pay a bit attention to the alkalinity, or carbonate hardness as its called over here. It is capable of altering the pH balance of your mix more that the possible urea will. At my place I have water from a well that gives an alkalinity of 250ppm. Fresh the pH is around 7 but that is due to dissolved CO2. after a while it attains values of 8-8.5. If I would use that for irrigation, it would totally dominate the pH given my fertiliser addition is at only some 200ppm. I try to control the pH of my irrigation water to be slightly below 6. That is easy by using rainwater, but with the well water I would probably run into trouble; as I did with my fresh-water aquarium. Its ok now



This is actually what I have been doing. I have hard water and I always try to bring down the ph to 6 using phosphoric acid. I took a sample of the drip water after three days and guess what, its 7.5 - 8.0. I think this is due to the calcium bicarbonates in the water. If this is the case then I take that the acidity is not a problem.


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## Rick (Mar 21, 2013)

Ray said:


> So do we know of K-eating bacteria we can seed the potting media with to clean it up?



There are not. They do not eat calcium either as Stone eluded to in a previous post.

Since I work in biological waste treatment the world would go crazy if someone came up with a bug that "consumes" the 4 major cations (Na, Ca, K, and Mg).

The bacteria (like plants and humans) need a very small amount of these materials for biomass. But that amount is insignificant compared to the amount of carbon consumed or the ammonia that is converted to nitrate by nitrifiers.

Yes nitrifying bacteria are different from general heterotrophic species, but are significant in potting media. They probably convert most of the ammonia to nitrate in a fert mix. The actually do not "consume" ammonia, but use it as a source of electrons (along with oxygen). Protons are a waste product of the reaction, and requires alkalinity OH and HCO3 (not calcium) to neutralize it (to keep from poisoning themselves out).

Nitrifying bacteria are the crux of municipal waste water treatment. These guys handle litterally tons of ammonia per day (converting to nitrate). Your basic aquarium opperates on the exact same principal to keep the ammonia produced by fish excreetion to pollute your home aquarium.

They are everywhere in damp soil conditions as long as pH is > 5.0 and O2 is present. They work in fresh and salt water. Temps almost to freezing and up to 30+C.


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## gonewild (Mar 21, 2013)

Rick said:


> They are everywhere in damp soil conditions as long as pH is > 5.0 and O2 is present. They work in fresh and salt water. Temps almost to freezing and up to 30+C.



Are they the same species or a huge amount of different species for differing conditions?


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## Rick (Mar 21, 2013)

Bjorn said:


> Guess its ammonia they eat  you have a point, provided your bacterial(nitrosomonas) population is high enough to oxidize enough of the ammonia. Guess the net reaction going from NH3 to NO3- is one H+ in excess? But if your pH is 5.5 or so then your nitrosomonas would not be very active or?  And of course enough Nitrobacter has to be present as well since we are not interested in nitrite that is the product of the nitrosomonas. Nitrobacter enjoy pH levels of slightly above 7 so perhaps they do not like the acid bark after all?
> Btw. I do water frequently, but drawing a comparison to aquariums is perhaps to exaggerate a bit oke:
> Joke aside;
> Another thing is the fact that those of you that uses well water should pay a bit attention to the alkalinity, or carbonate hardness as its called over here. It is capable of altering the pH balance of your mix more that the possible urea will. At my place I have water from a well that gives an alkalinity of 250ppm. Fresh the pH is around 7 but that is due to dissolved CO2. after a while it attains values of 8-8.5. If I would use that for irrigation, it would totally dominate the pH given my fertiliser addition is at only some 200ppm. I try to control the pH of my irrigation water to be slightly below 6. That is easy by using rainwater, but with the well water I would probably run into trouble; as I did with my fresh-water aquarium. Its ok now



Being in a company that specializes in biological waste water treatment, we've learned the limits of what nitrobactor and nitrosomonas are capable of. Actually they live in joint colonies proximal to each other. It is possible to kill one but leave the other alive, but since they noramally are found together the switch from NH3 to NO2 to NO3 is almost instantaneous, and for engineering purposes consider a single step. As noted earlier, every mg of NH3 converted to nitrate requres over 7mg of alkalinity (over 8 mg of bicarbonate) to neutralize the proton production. That's a fair amount of acidity produced. Also the pH at absolute 0 alkalinity in a system is a little over 4.0 su. So yes the efficiency of nitrification is reduced as pH goes down, but it is proportionate to the alkalinity availability (rather strictly pH). So you can still get nitrification at pH's below 6.0

I'm not sure if you have heard of wet/dry or trickle filters. Instead of having your bacteria colonizing submerged media in the aquarium, you grow your bacteria on a high surface media (often Leca!!) that you spray water over so it is wet but not submerged. The nitrifiers are much more efficient in this system. (and very analogous to a semi hydro orchid growing system).


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## Rick (Mar 21, 2013)

Bjorn said:


> Guess its ammonia they eat  you have a point, provided your bacterial(nitrosomonas) population is high enough to oxidize enough of the ammonia. Guess the net reaction going from NH3 to NO3- is one H+ in excess? But if your pH is 5.5 or so then your nitrosomonas would not be very active or?  And of course enough Nitrobacter has to be present as well since we are not interested in nitrite that is the product of the nitrosomonas. Nitrobacter enjoy pH levels of slightly above 7 so perhaps they do not like the acid bark after all?
> Btw. I do water frequently, but drawing a comparison to aquariums is perhaps to exaggerate a bit oke:
> Joke aside;
> Another thing is the fact that those of you that uses well water should pay a bit attention to the alkalinity, or carbonate hardness as its called over here. It is capable of altering the pH balance of your mix more that the possible urea will. At my place I have water from a well that gives an alkalinity of 250ppm. Fresh the pH is around 7 but that is due to dissolved CO2. after a while it attains values of 8-8.5. If I would use that for irrigation, it would totally dominate the pH given my fertiliser addition is at only some 200ppm. I try to control the pH of my irrigation water to be slightly below 6. That is easy by using rainwater, but with the well water I would probably run into trouble; as I did with my fresh-water aquarium. Its ok now



http://aem.asm.org/content/70/11/6481.short

Bjorn This is a new one on me. Efficient nitrification at pH 4.3!!! They are using a fixed film reactor (similar to WET/Dry, trickle system I mentioned earlier).


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## Stone (Mar 21, 2013)

Rick said:


> Actually lots of amino acid in kelp extract and glutamic acid is about the highest abundance of all of them.



I use this when I can get it:
http://www.ecoorganicgarden.com.au/v/vspfiles/assets/images/template/eco-aminogroLabel.pdf


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## Rick (Mar 21, 2013)

Stone said:


> I use this when I can get it:
> http://www.ecoorganicgarden.com.au/v/vspfiles/assets/images/template/eco-aminogroLabel.pdf



That's not bad looking. The difference between it and the kelp extract I use is that it has higher Ca and Mg than the K. Otherwise very similar.


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## Ozpaph (Mar 21, 2013)

Stone said:


> I use this when I can get it:
> http://www.ecoorganicgarden.com.au/v/vspfiles/assets/images/template/eco-aminogroLabel.pdf



Why do you use that?
Ive seen it at Bunnings.


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## Stone (Mar 21, 2013)

Ozpaph said:


> Why do you use that?
> Ive seen it at Bunnings.



:rollhappy:Our Bunnings sees fit not to stock it anymore


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## Bjorn (Mar 22, 2013)

Rick said:


> Being in a company that specializes in biological waste water treatment, we've learned the limits of what nitrobactor and nitrosomonas are capable of. Actually they live in joint colonies proximal to each other. It is possible to kill one but leave the other alive, but since they noramally are found together the switch from NH3 to NO2 to NO3 is almost instantaneous, and for engineering purposes consider a single step. As noted earlier, every mg of NH3 converted to nitrate requres over 7mg of alkalinity (over 8 mg of bicarbonate) to neutralize the proton production. That's a fair amount of acidity produced. Also the pH at absolute 0 alkalinity in a system is a little over 4.0 su. So yes the efficiency of nitrification is reduced as pH goes down, but it is proportionate to the alkalinity availability (rather strictly pH). So you can still get nitrification at pH's below 6.0



Thank you for explaining these things to me; but there arel details in your calculatuons that puzzles me: Please correct me if I am wrong. I am sincerely interested in understanding these issues a bit more in-depth. 
Although Nitrification involves exchange of quite a few electrons and protons the net reaction going all the way from NH3 to NO3- produces only one proton. That should be capable of eliminating one HCO3-. or; nitrification of one gram NH3 should be able to consume 3.6gram hydrogencarbonate. Or if you prefer: 4.8 g Calciumhydrogencarbonate. But, the latter is hardly available as such in the water I guessoke:
This use of alkalinity is another thing I do not really get the grip on: When you refer to alkalinity, is it as hydrogencarbonate or as carbonate? If it is as calciumcarbonate, the oxidation of one gram NH3 would neutralise 5.9 gram CaCO3 and not the 4.8 gram as predicted for calciumhydrogencarbonate.
Ok I have checked up a bit and it seems as if alkalinity is normally expressed as CaCO3. So If I used my well water of 250mg/l CaCO3 this is equivalent to approximately 2.5 mmol/l CaCO3. To neutralise that it would be necessary to have 2.5mmol/l ammonia from Urea that was converted to nitrate. Since urea decomposes to 2 NH3 this should be the same as 1.25mmol/l urea in the irrigation water which is equivalent to approximately 0.075 g/l. This equals to 75 mg/l. In this case I should not exceed 75mg/l urea in order not to acidify the mix. Or put differently: If I was using my well water and a fertiliser with 20%N from urea (=43%urea in the fertiliser) then any excess of 175ppm fertiliser would be capable of acidifying my mix. If everything was converted. Using a back mix of 1:10 with RO water should imply that some of that urea fertiliser(>17.5ppm urea fertiliser) would be beneficial. Of course if the urea is not 100% converted during its passage through the compost, more is needed.
The pH being 4 at no alkalinity is quite theoretical, it is totally dependent on the amount of dissolved solids and gases and as such highly variable. But due to CO2, it is normally acid and extremely hard to measure accurately.
PS: I found this one; at least for embryos of Cattleya, ammonium seems vital.
http://harvardforest.fas.harvard.ed...publications/pdfs/Raghavan_AmJBotany_1964.pdf
And this one explains it all:
http://forums2.gardenweb.com/forums/load/orchids/msg032222191547.html


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## Rick (Mar 22, 2013)

Bjorn said:


> The pH being 4 at no alkalinity is quite theoretical, it is totally dependent on the amount of dissolved solids and gases and as such highly variable. But due to CO2, it is normally acid and extremely hard to measure accurately.



However, the ASTM method for measuring alkalinity is a titration against a standardized acid solution, with the endpoint of pH 4.0~~ The titration and math are very easy to do.

Have you gone through this paper?

http://www.staugorchidsociety.org/PDF/IPAFertilizers.pdf


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## Rick (Mar 22, 2013)

Bjorn said:


> This use of alkalinity is another thing I do not really get the grip on: When you refer to alkalinity, is it as hydrogencarbonate or as carbonate? If it is as calciumcarbonate, the oxidation of one gram NH3 would neutralise 5.9 gram CaCO3 and not the 4.8 gram as predicted for calciumhydrogencarbonate.
> Ok I have checked up a bit and it seems as if alkalinity is normally expressed as CaCO3.



Bjorn Although expressed as CaCO3 equivalents, at the pH ranges and gas saturation levels we are working with, the predominat ion is bicarbonate (which I guess is what you are calling hydrogencarbonate, HCO3).

Calcium carbonate is esentially insoluble (until pH <<4.0) I can't get it to melt until pH 2.0 in a reasonable length of time. But if you want to generate measurable alkalinity fast, add some baking soda (NaHCO3) to some RO water, and the math is easy.

The conversion from alkalinity as CaCO3 to bicarbonate ion is just a factor of 1.22. So "alkalinity as CaCO3)"X1.22 will give you bicarbonate ion concentration.


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## Bjorn (Mar 22, 2013)

Rick said:


> However, the ASTM method for measuring alkalinity is a titration against a standardized acid solution, with the endpoint of pH 4.0~~ The titration and math are very easy to do.
> 
> Have you gone through this paper?
> 
> http://www.staugorchidsociety.org/PDF/IPAFertilizers.pdf



Yes it puzzles me too. Today it seems widely accepted that nitrogen is used by the plant for production of aminoacids, and those are synthesized from ammonium, not nitrate. Quite a few investigations show that ammonium is assimilated quicker than nitrate. This is probably because it immediately goes into aminoacid synthesis. Nitrate can be stored for later use so a mix gives best results. In several tests, ammoniumnitrate is the preferred over nitrate or ammonium. In soil, Bill Argos presentation is probably correct, if all ammonium gets oxidised, but I am uncertain whether it is applicable for orchids.
Take Fig. 1 for instance. It may be read as if urea splits into ammonium and two protons, while reality is that urea yields two ammonium and two protons. This is possibly the root of quite a few misunderstandings regarding this topic.

The end point of the titration is just a matter of convention. It was chosen so to represent a value to keep to doing quick tests on that matter. Making real titration curves gets very difficult as the point of equivalence gets smeared out due to all the other salts except calcium carbonate that sums up the alkalinity. As a curiosity can be mentioned monosilicic acid that is the silicon species that is absorbed by plants.


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## Bjorn (Mar 22, 2013)

Rick said:


> Bjorn Although expressed as CaCO3 equivalents, at the pH ranges and gas saturation levels we are working with, the predominat ion is bicarbonate (which I guess is what you are calling hydrogencarbonate, HCO3).
> 
> Calcium carbonate is esentially insoluble (until pH <<4.0) I can't get it to melt until pH 2.0 in a reasonable length of time. But if you want to generate measurable alkalinity fast, add some baking soda (NaHCO3) to some RO water, and the math is easy.
> 
> The conversion from alkalinity as CaCO3 to bicarbonate ion is just a factor of 1.22. So "alkalinity as CaCO3)"X1.22 will give you bicarbonate ion concentration.



I know that calcium carbonate essentially is insoluble, the use of it is again just a convention. Just like presenting NPK in the fertilisers. Nobody think that N is there as nitrogen and K is not there as metallic potassium.
The below link is describing many of these aspects in detail.
http://books.google.no/books?id=ytG...epage&q=nitrogen assimilation orchids&f=false


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## Rick (Mar 22, 2013)

Bjorn said:


> The end point of the titration is just a matter of convention. It was chosen so to represent a value to keep to doing quick tests on that matter. Making real titration curves gets very difficult as the point of equivalence gets smeared out due to all the other salts except calcium carbonate that sums up the alkalinity. As a curiosity can be mentioned monosilicic acid that is the silicon species that is absorbed by plants.



Sure, but at some point are we getting woried about a very small effect outside of the relevance to 90% of the world our plants live in?

The vast majority of life exists around water explained by only 7 major ions taking up 99% of the inorganic chemistry. Also the majority (certainly not all) of life opperates between pH 4-9. 

Generally we don't need to get to the precision of finding the Higgs to figure out most of natures operations. (at least in my GH)


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## Rick (Mar 22, 2013)

Bjorn said:


> In soil, Bill Argos presentation is probably correct, if all ammonium gets oxidised, but I am uncertain whether it is applicable for orchids.



That could be the focus of the issue since for one there are 30,000 species of orchids in almost as many different habitats, and secondly we are trying to grow orchids in conditions more applicable to potted mums.

From the handful of papers I have been able to find/read on orchids. It looks like offering a diversity of relatively low concentrations of N source is desirable. 

It doesn't take a lot of anything in particular. It seems like working at concentrations of N that are not environmentally relevant turn the exercise into a pot management exercise rather than a plant physiology exercise.


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## Ray (Mar 22, 2013)

1) Bill's article may have been in the IPA journal, but his background is in terrestrial plant nutrition, so those reactiuons are far more applicable to soils.

2) I am beginning to think that frequent, low concentrations are the keys.

The solutions reaching the plants are verry dilute - I have seen numbers of 5 ppm TDS for throughfall, and 25 ppm for "trunk flow". It makes sense that the first to cascade through would be the most concentrated, hence the "gold vein" the orchids would try to harvest. No too suprisingly, velamen has sites the immediately capture ionic species - I envision them as being the "baleen filtering the krill from the sea water".

So once those sites are occupied, it is not very efficient to dump more ions on them. Then, as it will take some amount of time for the trapped ions to be absorbed, a later-, but still dilute solution wil replenish the velamen.


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## Rick (Mar 22, 2013)

Ray said:


> So once those sites are occupied, it is not very efficient to dump more ions on them. Then, as it will take some amount of time for the trapped ions to be absorbed, a later-, but still dilute solution wil replenish the velamen.



I was looking at another corn article that seemed to come up with similar conclusion. Pulsed low nitrate input was better than constant dose. The hypothesis was that root uptake was fast, but the enzyme pathway (in the leaf/shoot tissues) just gets clogged up (backlogged) relatively fast, and idles until stored nitrate goes down.


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## Rick (Mar 22, 2013)

http://hortsci.ashspublications.org/content/27/6/680.6

If someone wants to buy the whole paper (or find it otherwise) this could be a good one.

These authors doubt the hypothesis that the bottleneck is the velamin, but indicate the relative low activity of the N utilizing enzymes in the tissues for the low uptake rates in orchids.

But its another paper that shows the importance of amino acid uptake in orchids as a significant source of N.


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## eggshells (Mar 22, 2013)

Rick said:


> http://hortsci.ashspublications.org/content/27/6/680.6
> 
> If someone wants to buy the whole paper (or find it otherwise) this could be a good one.




https://dl.dropbox.com/u/993342/680.6.full.pdf


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## Ozpaph (Mar 22, 2013)

eggshells said:


> https://dl.dropbox.com/u/993342/680.6.full.pdf



If you'd be so kind as to summarize the 944 abstracts for me that would be appreciated :rollhappy::rollhappy::rollhappy:


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## Stone (Mar 22, 2013)

Ray said:


> 1) Bil
> 
> 
> 
> ...


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## Ray (Mar 23, 2013)

Stone said:


> Yes all the chemistry is interesting (up to a point) but is will it grow better paphs? I don't think so A good p/mix and a bit of fertilizer in the correct moisture/environment. The simple method of sitting a few plants in a saucer of water did FAR FAR more than any combination of fertilizer ever could.


I think we may be ignoring the role of frequency of watering.

As Rick mentioned a while back, water and air are part of the makeup of the plant, too. 

> C, O, H, & N are present at levels of 1-7% of the overall mass (C is about 50% of the dry mass)
> Ca, Mg, P, K, & S in the 0.1-1% level
> Everything else is ppm's.

Watering not only provides chemical building blocks for the plants, but it tends to flush fresh air through the media at a rate faster than natural diffusion. I think that plays a role in Rick's basket culture observations.


Ray Barkalow
Sent using Tapatalk


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## Rick (Mar 23, 2013)

Ray said:


> I think we may be ignoring the role of frequency of watering.
> 
> (C is about 50% of the dry mass)
> 
> ...



Yes and since that carbon is hydrolized, the carbon products (i.e mostly celulose, sugars) make up about 95% of the dry mass. N is incorporated into carbon structures at 3% of the total dry mass.


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## Rick (Mar 24, 2013)

http://www.ncbi.nlm.nih.gov/pubmed/16667499

Ok for the mechanistic folks.

This article shows that the optimal pH for Nitrate Reductase in spinach is 7.0, and is also suppressed by higher ionic strength (TDS).

Nitrate reductase is the enzyme pathway responsible for reducing nitrate to ammonia in plants so it can be used to make amino acids.

the article also contrasts the NR activity in spinach with that of a unicellular algae (which operates more efficiently at a higher pH and TDS).

This means that different plants can have different optimal pH/TDS conditions for nitrate use. Which should be based on the natural/ecological conditions they are evolved to be in. Orchids are generally found in low ionic strength environments, so I wouldn't expect their nitrate reductase system to operate more like chlorella than spinach. 

Also these are cellular conditions in this paper, not pot conditions. But if pot conditions are extreme, its hard to meet cell conditions. If you add a bunch of bicarbonate to a pot its going to be hard for the cell conditions to stay maintain a pH of 7.


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