Fertilizer TDS Nutrition and Watering

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NYEric

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I got a Urea free formula but I mix it 1:1 w/ a formula that has urea. [I stopped using this for my Phrags though, and went to a weak MSU solution.] I think I have to up my fertilizer routine a little because I do have so much light and energy in the growing area. I guess my method differs from Lance's because my plants are always in the water solution.
 
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gonewild said:
I've never had problems with Ammonium nitrate, when applied correctly, but I prefer Calcium nitrate and Potassium nitrate as sources for nitrogen on delicate potted plants.

Sometimes you might want to limit the potassium or calcium in your nutrient solution and Ammonium nitrate is really the other good source.

Do you know what were the specific problems he had?

I misspoke when I mentioned ammonium. It is just NO3 (nitrate) that was mentioned. Nothing specific other than it typically caused death in paphs and the gentleman mentioned as the main source of the info.
 

Ray

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Lance's recommendation about calibrating a TDS meter is a good one, although I'm not sure I'd use table salt to do so. (Then again, I don't know how much it really matters, so he could be close enough.)

TDS meters just measure electrical conductivity of the solution and add an arbitrary conversion factor. EC is determined by the ionic mobility of the dissolved species. If you add table salt to pure water, the only things contributing to the EC are Cl- and Na+, which are both small in diameter so move easily in the solution. An ion of the same size but twice the charge moves twice as fast, while one with twice the size and the same charge moves half as quickly. Because of those ionic mobility differences, that conversion factor needs to be different depending on the exact chemical makeup of the solution.

Using the EC and concentration data from Blackmore, and a conductivity standard, I calibrated my two meters. At 150 ppm N of the MSU RO formulation, the calculated TDS contribution from the fertilizer should be about 425 ppm. My two meters told me about 600 and 750!

That is not a problem, however, as I now know that if I measure the TDS at those levels, I am really getting the 150 ppm N. If, on the other hand, I use them and see 425 ppm and trust it at face value, I'm actually underfeeding.
 

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dave b said:
From an environmental standpoint, nitrates (NO3) can be easilly washed away from yards, golf courses, and farm fields. It ends up in our rivers, and ground water supplies which is not good. It can contribute to unnattural algae blooms, and even build to toxic levels killing fish and other organisms. Most fertilizers provide N in 3 ways. Ammonium (NH4)...its safer, because it cant wash away easier in soils, it is also converted to NO3 (second method) by bacteria. And third, urea. Some research suggests that urea bound N is not available unless in soils where beneficial bacteria / fungi can break it down to usable sources. many orchid fertilizers will state that they dont use urea based N because of this. Our orchid medias dont harbor the necessary microorganisms.

Whether i answered your question, is another story.

I work with these materials allot as an aquatic toxicologist. Ammonia is a very toxic compound compared to nitrate. Its toxicity is pH dependent. The higher the pH the more toxic, with the highest toxicity in the pH range of 8-9 s.u. (generally out of soil pH ranges). The toxicity of nitrate is orders of magnitude less than for amonia and its first bio-oxidation product nitrite. Orchids will utilize ammonia and nitrate fairly well as nutrients, but the levels to achieve toxicity (as opposed to growth) will be less for amonia than nitrate. Subsequently it may be argued that the best source of nitrogen for orchids would be calcium nitrate. Your are correct that urea cannot be utilized by plants without microbial intervention. Urea fertilizers are popular with agri-crop species with lots of soil bacteria present.
 

gonewild

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Rick said:
I work with these materials allot as an aquatic toxicologist. Ammonia is a very toxic compound compared to nitrate. Its toxicity is pH dependent. The higher the pH the more toxic, with the highest toxicity in the pH range of 8-9 s.u. (generally out of soil pH ranges). The toxicity of nitrate is orders of magnitude less than for amonia and its first bio-oxidation product nitrite. Orchids will utilize ammonia and nitrate fairly well as nutrients, but the levels to achieve toxicity (as opposed to growth) will be less for amonia than nitrate. Subsequently it may be argued that the best source of nitrogen for orchids would be calcium nitrate. Your are correct that urea cannot be utilized by plants without microbial intervention. Urea fertilizers are popular with agri-crop species with lots of soil bacteria present.

Urea releases ammonia as a gas when it is in contact with the atmosphere so based on what you say that is even more reason to avoid it.
 

gonewild

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Ray said:
Lance's recommendation about calibrating a TDS meter is a good one, although I'm not sure I'd use table salt to do so. (Then again, I don't know how much it really matters, so he could be close enough.)

TDS meters just measure electrical conductivity of the solution and add an arbitrary conversion factor. EC is determined by the ionic mobility of the dissolved species. If you add table salt to pure water, the only things contributing to the EC are Cl- and Na+, which are both small in diameter so move easily in the solution. An ion of the same size but twice the charge moves twice as fast, while one with twice the size and the same charge moves half as quickly. Because of those ionic mobility differences, that conversion factor needs to be different depending on the exact chemical makeup of the solution.

Table salt is good to use to calibrate a meter because it is something everyone has. When mixed at exact ratios it provides an accurate known ppm to calibrate by.

It is not practical to have a seperate meter adjusted for each fertilizer element. It is also not reasonable to expect hobbyist growers to spend $300 on an accurate ec meter. So what we need to do is talk in terms of readings from ppm testers that everyone can afford ($20-$30). When calibrated to a table salt solution the accuracy is good enough to use for growing plants.

The cheap ppm tester I bought came calibrated very accurately and I felt no need to adjust it or compensate for the error.

Using the EC and concentration data from Blackmore, and a conductivity standard, I calibrated my two meters. At 150 ppm N of the MSU RO formulation, the calculated TDS contribution from the fertilizer should be about 425 ppm. My two meters told me about 600 and 750!

How did you make the fertilizer solution you tested? Measuring by weight or volume?

Above you say with 150 ppm N the total is 425 ppm.
On your web page you say 125 ppm N is 475 ppm total.

You written numbers don't support each other, can you define which is correct?

This is a quote from your website:
"As I typically shoot for 100-125 ppm N in my fertilizer solution, I simply use my TDS meters as a check, knowing that the Hanna TDS1 should show between 380 and 475 ppm TDS,"

That is not a problem, however, as I now know that if I measure the TDS at those levels, I am really getting the 150 ppm N. If, on the other hand, I use them and see 425 ppm and trust it at face value, I'm actually underfeeding.

I think the best thing for most folks to do is to trust the label on the fertilizer to start with. Then use the meter to make sure the concentrations in their pots are remaining at a safe level.

If you want to maintain 150 ppm of nitrogen and use a meter to keep track of the concentration here is a plan to follow....

(choose your desired nitrogen level, 150 ppm is used as an example only)

1. Make a table salt solution to calibrate your test meter. Save this solution to check your test meter in the future. Make a note as to what reading the meter gives for future reference

2.The label on the MSU (13-3-15) says to use 1 tsp per gallon to get 150 ppm. Use 1 tsp per gallon and trust it is correct.

3. Measure the total ppm with your test meter and remember this as the total ppm.

4. Periodically check the water in your pot reservoir or the small amout of water that drains from the pot with the same test meter to see how it compares to the original total. If your ppm levels remain at or near the original level you are basically fertilizing correctly. If your levels are contstantly lower either your plants are consuming the nutrients or you are adding fresh water that dilutes the solution in the pot. If the concentration is lower you can safely increase the amount of fertilizer you are using. If the concentration is higher you should flush the media more often.

5. Occasionally test your meter by taking a reading of your saved table salt solution you made in step #1. If the meter no longer reads the same as when you first tested the solution you need to calibrate your meter's readout or get a new meter. If it is only of by a small amount don't worry about it.
 

dave b

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Rick said:
I work with these materials allot as an aquatic toxicologist. Ammonia is a very toxic compound compared to nitrate. Its toxicity is pH dependent. The higher the pH the more toxic, with the highest toxicity in the pH range of 8-9 s.u. (generally out of soil pH ranges). The toxicity of nitrate is orders of magnitude less than for amonia and its first bio-oxidation product nitrite. Orchids will utilize ammonia and nitrate fairly well as nutrients, but the levels to achieve toxicity (as opposed to growth) will be less for amonia than nitrate. Subsequently it may be argued that the best source of nitrogen for orchids would be calcium nitrate. Your are correct that urea cannot be utilized by plants without microbial intervention. Urea fertilizers are popular with agri-crop species with lots of soil bacteria present.

Great info, good to have an expert on hand. You've got me wondering now. Is the ammonia (NH3) in the nitrogen cycle you mentioned (bio-oxidation) interchangeable with the ammonium (NH4) of fertilizers? I know enough to only be dangerous. Ammonia is broken down by bacteria which produce the nitrite, then by another to nitrate. Is ammonium broken down in the same manner? Do they contribute N in the same way to plants? Forgive me if im starting to get too far out into left field.
 

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You've picked up on the bio-oxidation pathway that aquarists and waste-water treatment engineers have been utilizing for years for amonia management. The conversion from amonia to amonium is a pH dependent process that also is important since the higher the pH the higher the percentage of unionized amonium (the most toxic form) ion is available. Therefore regardless of what the bottle says is the form of ammonia (NH3, or NH4+) it will change from one form to another in a ratio that is pH and temperature dependent. Another way to get rid of amonia from water is to raise the pH to 10 (to convert all the amonia to the volitile unionized form) and airstrip it off.

Nitrifying bacteria need an alkalinity source (i.e moderate pH environment) to dump the hydrogens from the ammonia as they oxidize it to nitrite and then nitrate, but if you raise the pH up to high the percentage of toxic amonia goes up to much and kills them too. if the pH drops to low they can't nitrify, and the amonia goes untouched. Much of this is irrelavent to orchids and fish that don't nitrify, but experience ammonia toxicity primarily on the basis of the percent of free ammonia as the pH goes up.
 

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The industry (or ASTM) standard for calibrating conductivity meters is with potassium chloride at 25C. But sodium chloride is a pretty stable standard too, especially in the temperature range we grow our plants in.

There are 2 different algorithems that are used in TDS meters to convert from conductivity to TDS. Most use a TDS based on sugar (I think sucrose). Others use NaCl. I don't know of any "TDS" meters that use both or have an option to use one or the other, but as pointed out in several prevous posts, the algorithm is an approximation to aqueous mixtures of salts where the conductance vs concentration of various salt species varies with the individual salt species. The ASTM method for determining TDS is to evaporate all the water from a measured quantity of solution and weigh the resulting residue of salts left. Meters are much faster, and can obviously used on the spot compared to the ASTM method. So in most cases a TDS meter calibrated to NaCl is close enough for orchid use.
 

Ray

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Lance,

As I said, you might be right about the calibration with salt. I guess my chemistry and engineering background forces me to question it - I did say that I don't know it's wrong!

TDS is a mass-per-mass measurement. I did some calculating from fertilizer labels. One gram of fertilizer contains the following grams of nutrients:

Greencare "MSU" Pure Water - 0.374427
Greencare "MSU" Well Water - 0.406099
Dyna-Gro "Grow" - 0.181006
Dyna-Gro "Bloom" - 0.162799

There are several problems with converting those values to TDS. For one, many of the listed nutrients are expressed as elements, so without "backing" your way into the formula of ingredients, you really don't know how much is contributed by the rest of the minerals that contributed the element. With Dyna-Gro we know that much of the formula is water, but in the powders, we're not taking into account 60%!

Then there's the question of how many grams in a teaspoon, and how inaccurately we measure teaspoons. 425 ppm or 475 ppm is irrelevant considering.

All that said, I believe it's best to control your fertilizer concentration by EC, not TDS. Doing some digging among professional growers and several fertilizer producers, I have learned that apparently we orchid growers are somewhat unique in the use of TDS rather than EC. I wonder why?
 
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Ray said:
All that said, I believe it's best to control your fertilizer concentration by EC, not TDS. Doing some digging among professional growers and several fertilizer producers, I have learned that apparently we orchid growers are somewhat unique in the use of TDS rather than EC. I wonder why?
The cost of taking the measurement, maybe?:confused:
 

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Ray said:
As I said, you might be right about the calibration with salt. I guess my chemistry and engineering background forces me to question it - I did say that I don't know it's wrong!

Well there really is no right or wrong with which salt you choose to make a calabration solution as long as it is mixed at an exact amount. I suggest table salt because everyone has it in the kitchen. To use a lab solution people have to purchase it. I just think for hobby growers it is best to keep it as simple and easy as possible.

TDS is a mass-per-mass measurement. I did some calculating from fertilizer labels. One gram of fertilizer contains the following grams of nutrients:

Greencare "MSU" Pure Water - 0.374427
Greencare "MSU" Well Water - 0.406099
Dyna-Gro "Grow" - 0.181006
Dyna-Gro "Bloom" - 0.162799

I would have thought the Pure Water formula would have had more nutrients per gram than the Well Water formula. So with the Dyna grow you get quite a bit less value for your money$

There are several problems with converting those values to TDS. For one, many of the listed nutrients are expressed as elements, so without "backing" your way into the formula of ingredients, you really don't know how much is contributed by the rest of the minerals that contributed the element. With Dyna-Gro we know that much of the formula is water, but in the powders, we're not taking into account 60%!

This is exactly why I suggest people trust the label recommendations for the amount to mix per gallon. Perhaps the MSU formula has more reason to trust it since they did such an extensive trial to develop the recipe. Once you have made the recommended mix you can establish the PPM(TDS) total. It does not really matter whether the meter total says 500 ppm or 600 ppm as long as the nutrient balance is correct and the total salts are not dangerously high for the plants you are using it on.

Then there's the question of how many grams in a teaspoon, and how inaccurately we measure teaspoons. 425 ppm or 475 ppm is irrelevant considering.

When I started using the MSU formula I measured it in grams to establish my benchmark concentration. The accuracy of teaspoon measurement can be off by several hundred ppm, this is another reason to test the ppm often. But 500 ppm is well under the danger level for most plants.

All that said, I believe it's best to control your fertilizer concentration by EC, not TDS. Doing some digging among professional growers and several fertilizer producers, I have learned that apparently we orchid growers are somewhat unique in the use of TDS rather than EC. I wonder why?

The reason we orchid growers use tds or ppm meters is because they cost $30 instead of $300. We would rather buy plants. Professional growers and consultants need nice toys to impress themselves and their clients. Now nobody take offense. ;)

EC and TDS are really the same thing. Just a different name for the same amount of electroconductivity. 1 EC = 500 ppm of NaCl.
PPM or TDS just converts the reading into an easy to relate to measurement.
In the past I have always used EC meters. Not until I returned from Peru did I even know you could buy an inexpensive meter that read in PPM. I bought one to try it out and found it is accurate enough to use for growing orchids.

It is like the speedometer on a car being in mph or kph or which measurement do you use in the kitchen 1 cup or 8 oz?
 
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IdahoOrchid

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gonewild said:
1 EC = 500 ppm of NaCl

Is this related to conductivity in electronics: ie E = I * R (Ohms Law) Voltage = Current * Resistance

I assume that EC would be related to the current portion ( the I ) in that formula. If so, how does it relate?
 

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IdahoOrchid said:
Is this related to conductivity in electronics: ie E = I * R (Ohms Law) Voltage = Current * Resistance

I assume that EC would be related to the current portion ( the I ) in that formula. If so, how does it relate?

Not only is it related, that is exactly what it is. The resistance between two probes at a fixed distance is measured in microsiemens which can be converted into OHMS or volts or EC or PPM or any other way you want to express the result.

Here are a couple of web pages that explain the basics of Electro conductivity measurement:

http://www.octiva.net/projects/ppm/

http://www.reefkeeping.com/issues/2004-04/rhf/feature/index.php
 

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Heather said:
I don't think people understand EC, I know I don't, so I go by TDS which I actually understand.

People have explained it to me ad nauseum, but I just don't get it. I'm too visual.

It is easier to relate to TDS (PPM) than EC because it is volume related as opposed to electrical current.

I don't think it is worth the time trying to understand the difference.

Use whatever meter you have or can afford to check the levels of your fertilizer solution and the solution in your pots. It does not matter what read out formula the tester shows. The point is to be able to keep your nutrient levels correct by detecting and comparing changes that might occur.

Just remember when you take advice from someone about fertilizer solutions to make sure that your meter speaks the same language as theirs.
For example, If I tell you to use "10 on the meter" make sure if I mean 10 PPM or 10 EC. There is a huge difference.
If I were to tell you to mix your MSU fertilizer to a total strength of 1.0 EC how would you ever know how many teaspoons to start with? But if I told you to mix it to a total strength of 500 ppm you could probably figure out from the fertilizer label to start with about 1 teaspoon.
 

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gonewild said:
It is easier to relate to TDS (PPM) than EC because it is volume related as opposed to electrical current.

I don't think it is worth the time trying to understand the difference.

Thanks Lance, that's sort of how I look at it too. I have a very hard time understanding things I cannot visualize (definitely a visual learner!) so things like this (and MATH!) have always been really difficult for me. You could explain it to me until you were blue in the face but I still wouldn't get it. I wish that teachers had understood about multiple intelligences back when I was in elem/middle/high school.
 

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Heather said:
Thanks Lance, that's sort of how I look at it too. I have a very hard time understanding things I cannot visualize (definitely a visual learner!) so things like this (and MATH!) have always been really difficult for me. You could explain it to me until you were blue in the face but I still wouldn't get it. I wish that teachers had understood about multiple intelligences back when I was in elem/middle/high school.

Great, so just use your meter to help give you clues why your plants look the way they do. The very best growers grow visually and only use meters to prevent future problems before they become visual..

Meters are for comparing information either from your own memory or to help you make decisions based on other peoples experience.

A doctor does not need a thermometer to determine if a patient has a temperature. But he may want to know if the fever is a 101For 104F.(does not matter if he reads it in Fahrenheit or Celsius as long as he knows which it is does it?)
 
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