The Cal-Mag of my dreams?

[MikeInOz]

**********Addendum Addendum addendum!!!*********
In an earlier post I mentioned the standard for Mo in hydroponics was 0.5ppm This is WRONG. I was supposed to write 0.05ppm. 10 times less Mo!
Everyone please make the necessary alterations in your notes!!
Note.... This is for the FINAL dilution given to the plants. Apologies for the oversight!
Sorry Steve, you may have to change your notes in the ferts explained section. The 0.0009% = 0.9ppm. Plenty! (or does it say 0.00009%? = 0.09ppm - still ok) Turns out you don't need to do anything.
What a balls up!
Here is a good converter....https://www.rapidtables.com/convert/num ... rcent.html

[Steve Johnson]

**********Addendum Addendum addendum!!!*********
In an earlier post I mentioned the standard for Mo in hydroponics was 0.5ppm This is WRONG. I was supposed to write 0.05ppm. 10 times less Mo!
Everyone please make the necessary alterations in your notes!!
Note.... This is for the FINAL dilution given to the plants. Apologies for the oversight!
Sorry Steve, you may have to change your notes in the ferts explained section. The 0.0009% = 0.9ppm. Plenty! (or does it say 0.00009%? = 0.09ppm - still ok) Turns out you don't need to do anything.
What a balls up!
Here is a good converter....https://www.rapidtables.com/convert/num ... rcent.html

Hi Mike,

Thanks for the correction. Per Dyna-Gro's specs, .0009% Mo in the 7-7-7 x 10,000 = 9 ppm. Diluting 1/2 tsp. per gallon of watering solution --- 9/1536 = .006 ppm = 6 ppb. Since your corrected target should be .05 ppm (50 ppb), let's do the math for a half-gallon of stock solution with Sodium molybdate:

0.1 gram Na2MoO4 = .0395 g. Mo
0.5 gal. = 1.892705892 L, and the Calculate This ppm calculator (https://calculate-this.com/ppm-of-solut ... lator#calc) gives us 20.87 ppm Mo in a half-gallon of stock solution. The next step is calculating the amount of stock solution per gallon of watering solution:
1 gal. = 768 teaspoons
20.87 ppm/768 = 0.0272 ppm (27 ppb)
That's 1 tsp., so if you add 2 tsp. of stock solution, you'll have 54 ppb Mo in your gallon of watering solution.

I was off by a factor of 10 in part 2 of my "Fertilizers explained" presentation, but easy enough to change it. Please check my math here before I do. I need to get a digital scale reading in 10ths of a gram anyway -- not expensive and easily available on Amazon. A little bit sure goes a long way, doesn't it?

By the way, RapidTables confirms -- .0009% = 9 ppm. I also took the liberty of making the necessary corrections in part 2 of the presentation.

[Steve Johnson]

I'm fascinated by how and why things work, so I was thinking about this with regard to the Nitrate N-Mo connection. The following is just a theory, so please feel free to shoot it down...

Since I'm fertilizing my cacti every time they get watered in the growing season, they receive 14 ppm NH4 and 32 ppm NO3 per feeding. Here's the theory:

NH4 = "fast release" that gets absorbed and used up by the plant in a few days. NO3 = "slow release" as NO3 is slowly reduced to NH4 used up by the plant in 1-2 weeks. That's where Mo comes in for the reduction process -- 6 ppb just from the Dyna-Gro = inefficient reduction leaving a significant part of the NO3 in the plant's tissues. 54 ppb coming from the Sodium molybdate stock solution I described in detail with my last post + 6 ppb from the Dyna-Gro (60 ppb Mo total) = efficient reduction, leading to more sustained and better growth. Hard to believe that such a tiny increase in Mo could make such a big difference, but if my theory is correct, a growing season with the Sodium molybdate supplement will show noticeable improvements in some cacti that could be Mo-deficient. After doing very close observation of those plants, I now know what to look for.

[ohugal]

Regarding the Molybdenum, is it not quite important to have scale that can read 0,01 gr. accurate? Or have a 0,1 ml accurate pipette when you decide to create a stronger concentrated stock solution of Molybdenum (Na2MoO4)? I haven't made a calculation yet, but what happens if you (accidentally) make a 0,19 gr. per 1/2 gallon Molybdenum stock? If your scale is only 0,1 gr. accurate you don't really know if you're overdosing or not. Or is this possible fluctuation acceptable give the fact Mo readily flushes out? I think I read that somewhere here on the topic.

[jerrytheplater]

Regarding the Molybdenum, is it not quite important to have scale that can read 0,01 gr. accurate? Or have a 0,1 ml accurate pipette when you decide to create a stronger concentrated stock solution of Molybdenum (Na2MoO4)? I haven't made a calculation yet, but what happens if you (accidentally) make a 0,19 gr. per 1/2 gallon Molybdenum stock? If your scale is only 0,1 gr. accurate you don't really know if you're overdosing or not. Or is this possible fluctuation acceptable give the fact Mo readily flushes out? I think I read that somewhere here on the topic.

You are talking about calculating % error. A scale which reads 0.1 gram, depending on the internal software, could actually be seeing anywhere from 0.051 to 0.149 gram. Calculate based on those numbers.

Getting reliable measurements for small numbers is expensive. It is better to do multiple dilutions to get the finer numbers. Say 10.0 gram per liter. Then take 100 ml of it and place in a new liter. Now you have 1.0 gram per liter. Now take 100 ml of the second liter and place in a third liter. Now you have 0.1 gram per liter. Now take 100 ml of it into a fourth liter and you have 0.01 gram per liter. And so on, depending on how far you have to go.

[Steve Johnson]

It might be helpful if we spend some time doing product research online...

From Amazon US:

https://www.amazon.com/gp/product/B0885 ... AF1V8&th=1

Thinkscale reads all the way down to .001 gram, so I think that should be precise enough for our purposes. And it costs the princely sum of -- $20. I already have one in my shopping cart. If our European friends need an equivalent, you can find it on Amazon Germany:

https://www.amazon.de/-/en/Precision-Mi ... r=8-5&th=1

Regarding the Molybdenum, is it not quite important to have scale that can read 0,01 gr. accurate? Or have a 0,1 ml accurate pipette when you decide to create a stronger concentrated stock solution of Molybdenum (Na2MoO4)? I haven't made a calculation yet, but what happens if you (accidentally) make a 0,19 gr. per 1/2 gallon Molybdenum stock? If your scale is only 0,1 gr. accurate you don't really know if you're overdosing or not. Or is this possible fluctuation acceptable give the fact Mo readily flushes out? I think I read that somewhere here on the topic.

IMO the scale from Amazon Germany would be perfect for you, so that takes care of the concerns you expressed re. accuracy. If you haven't seen it already, part 2 of my "Fertilizers explained" presentation has a metric calculation for making the stock solution -- and this applies to all liquid fertilizers with 7% N:

0.1 g Sodium molybdate contains .0395 g Mo
.0395 g/L of stock solution = 39.5 ppm Mo

1.5 mL stock solution per liter of watering solution gives you 59 ppb Mo going into the roots of your cacti. Not sure why you would want a more concentrated Sodium molybdate stock solution unless...

Or is this possible fluctuation acceptable give the fact Mo readily flushes out? I think I read that somewhere here on the topic.

I believe you were talking about an exceptable range. "I think I read that somewhere here on the topic" -- that would be Mike:

One more thing, Mo is leached readily (just as nitrates phosphates and sulphates) and it's availability is lowered as pH falls.

If the grower's potting medium is acidic to begin with, I have a feeling that Mo should be higher to compensate for the leaching. How much, I really don't know. My hydroponic mix is slightly alkiline, but I have to acidify my tap water. Final pH of the watering solution starts out at about 5.5, but it slowly rebounds up to 7.0 by the time the mix is completely dried out. Should I increase the amount of Sodium molybdate in my stock solution to compensate for leaching too? If so, how much? Once again, I really don't know. All I can go by are these quotes I included in my January 24 post:

From Promix (https://www.pthorticulture.com/en/train ... t-culture/):

• "Molybdenum toxicity is very rare and, in some crops, the tissue can have several thousand ppm and still not show symptoms. In a few rare cases there has been report golden yellow appearance of the leaves."

From Gardening Know How (https://www.gardeningknowhow.com/garden ... bdenum.htm):

• "Plants can tolerate very high levels of molybdenum but do poorly with little to none of the element."

I realize that the quotes refer to nonxeric plants, and they don't give us any hard numbers on toxicity levels. My intuitive hunch tells me that we could go quite a bit higher before Mo toxicity in cacti becomes a problem. But hunches don't give us a number we can use. The idea is to make things as simple and easy as possible for everyone, and it would be awfully nice to get a number that'll work for all growers regardless of whether or not leaching will be involved when they water their cacti. Any thoughts on this, Mike?

Speaking of...

**********Addendum Addendum addendum!!!*********
In an earlier post I mentioned the standard for Mo in hydroponics was 0.5ppm This is WRONG. I was supposed to write 0.05ppm. 10 times less Mo!

You were right the first time:

I don't have much time at the moment but this might help. All hydroponic solutions for various crops contain 0.05ppm Mo.

[ohugal]

Ok. Thanks guys.
Since we're adding such a small amount of sodium molybdate I thought it to be important we get that number right. The subsequent questions rather came from a 'what if' point of view. I already checked for scales which measure 0,01 gr. accurate. There are indeed pocket scales available for very decent prices which do just that.
If you don't want to buy one I think Jerry provides a good alternative method.
Jerry also informed me sodium molybdate becomes toxic to animals at a level of 0,3 ppm (causing copper deficiency), but it seems plants can take a lot more.
Regarding soil pH and Molybdenum I found the following article after a quick search: http://corn.agronomy.wisc.edu/Management/pdfs/a3555.pdf

[Steve Johnson]

Regarding soil pH and Molybdenum I found the following article after a quick search: http://corn.agronomy.wisc.edu/Management/pdfs/a3555.pdf

The information in that article is quite valuable, so thank you for sharing it with us! I now have it on my computer, and I'll read it carefully a good number of times over the weekend, absorb the lessons learned, then see if we can come up with a rational amount of Sodium molybdate that's higher than what we've been discussing. Toxicity to animals is duly noted, so common sense indicates that we need to store and keep the chemical safely away from pets at all times.

Note to Mike: The article discusses crops growing in the open ground, so I don't know if there's much (if anything) we can extrapolate given the fact that we're growing cacti in pots. Given your horticultural expertise, IMO it would be better if we defer to your informed opinion on the matter after you read it. As I said earlier -- the idea is to make things as simple and easy as possible for everyone, and it would be awfully nice to get a number that'll work for all growers regardless of whether or not leaching will be involved when they water their cacti.

[jerrytheplater]

It might be helpful if we spend some time doing product research online...

From Amazon US:

https://www.amazon.com/gp/product/B0885 ... AF1V8&th=1

Thinkscale reads all the way down to .001 gram, so I think that should be precise enough for our purposes. And it costs the princely sum of -- $20. I already have one in my shopping cart.

I read over that pocket scale Steve. It is a good value for its price. I would get one too. It is a throw away device. Chuck it in the can when it breaks. I like that it can be calibrated and the weight is included. Be careful not to touch the weight with your bare hands. You don't want it to corrode (if brass) or get dirty.

Cons:
Accuracy good to +-0.005 gm or 5 mg. So, you can be sure you can measure to 0.01 gram very confidently. That would be 0.005 to 0.015 gram in its range of accuracy. Steve was weighing 0.1 gm. That would be 0.095 to 0.105 gram. Good enough.

Capacity is only 50 grams. For the Mo measurements, this is fine. But you will want to use it for other things eventually. That 50 gm includes any container you are measuring into, so just remember that. Remember that powders will stick to your container or measuring papers. You need to wash the powder off to get all that you weighed. I don't know the weight where the scale will be damaged by an overweight object.

Remember also that your fingerprints have a weight. I weighed mine on a clean glass beaker and got about 6 mg. That is why gloves are needed. Non static are best, like cotton. Good chance you will see static electricity affecting this scale. I had a lab grade mg scale costing $8,000.00 at work. Good to +- 0.0005 gm. Capacity of 500 grams. Static would deflect the scale from a few inches away. Even me shifting my body position would change the level of the scale and effect the reading. Forget about touching the lab bench while weighing.

[Steve Johnson]

Good to know, Jerry. The microscope sales and service company I work for sent me 2 big boxes of medical gloves when the COVID-19 pandemic hit in 2020. It was a requirement to wear them when we service scopes in hospitals, although not so any more, and I can keep the box I have left for personal use. I'll be sure to wear the gloves when I touch the weight. By the way, that Thinkscale I'm buying will come in handy when I whip up another gallon of Potassium sulfate stock solution. I was measuring it with a digital postal scale not reading in 10ths of a gram, so I'll get a more precise measurement next time.

Hopefully Mike will chime in on my last post -- I'd rather not guess about whether we should increase the amount of Sodium molybdate for a reliable stock solution that'll work for everyone.

[MikeInOz]

You were right the first time:

I don't have much time at the moment but this might help. All hydroponic solutions for various crops contain 0.05ppm Mo.

I went back and changed it.

[MikeInOz]

Note to Mike: The article discusses crops growing in the open ground, so I don't know if there's much (if anything) we can extrapolate given the fact that we're growing cacti in pots. Given your horticultural expertise, IMO it would be better if we defer to your informed opinion on the matter after you read it. As I said earlier -- the idea is to make things as simple and easy as possible for everyone, and it would be awfully nice to get a number that'll work for all growers regardless of whether or not leaching will be involved when they water their cacti.

Steve, because we grow our plants in media which is far more open than soil in a limited volume compared with the open ground and the leaching from watering will be higher AND our growing media tends to be more acidic than soils, I think we should basically look at it as growing hydroponically and stick to the 0.05ppm Mo in the final dilution of the fertilizing solution. Whether it is 0.03 or 0.08 probably doesn't really matter that much. Given that Mo deficiency is found first in older leaves, it means that it is mobile in the plant and gets moved to where it is needed and because cacti are such store houses, as long as there is some coming to the plant when it is growing it should have enough for it's purposes. Problems might occur when a cacti is growing for a long time in one pot, the media is acidified and no Mo is given. Especially if mostly nitrate N is given without Mo. If someone happens to have a cactus in a pot growing in the old ''1 soil, 1 leaf, mold 1 sand'' type of mix, it would be extremely unlikely that it would suffer from a lack of Mo. With our more open and lean modern mixes, we need to be a bit more attentive.

[Steve Johnson]

Hi Mike,

I'm still concerned about this:

One more thing, Mo is leached readily (just as nitrates phosphates and sulphates) and it's availability is lowered as pH falls.

If the grower's potting medium is acidic to begin with, I have a feeling that Mo should be higher to compensate for the leaching. How much, I really don't know. My hydroponic mix is slightly alkiline, but I have to acidify my tap water. Final pH of the watering solution starts out at about 5.5, but it slowly rebounds up to 7.0 by the time the mix is completely dried out. Should I increase the amount of Sodium molybdate in my stock solution to compensate for leaching too? If so, how much? Once again, I really don't know. All I can go by are these quotes I included in my January 24 post:

From Promix (https://www.pthorticulture.com/en/train ... t-culture/):

• "Molybdenum toxicity is very rare and, in some crops, the tissue can have several thousand ppm and still not show symptoms. In a few rare cases there has been report golden yellow appearance of the leaves."

From Gardening Know How (https://www.gardeningknowhow.com/garden ... bdenum.htm):

• "Plants can tolerate very high levels of molybdenum but do poorly with little to none of the element."

I realize that the quotes refer to nonxeric plants, and they don't give us any hard numbers on toxicity levels. My intuitive hunch tells me that we could go quite a bit higher before Mo toxicity in cacti becomes a problem. But hunches don't give us a number we can use. The idea is to make things as simple and easy as possible for everyone, and it would be awfully nice to get a number that'll work for all growers regardless of whether or not leaching will be involved when they water their cacti.

Any thoughts on the matter?

[MikeInOz]

Hi Mike,

I'm still concerned about this:

Should I increase the amount of Sodium molybdate in my stock solution to compensate for leaching too?

No. Leaching occurs all the time but is only a problem if the nutrient is not replaced by fertilizer. Leaching leading to a lack of Mo will only occur in acid, open media which do not receive enough or any Mo.
As for pH, You don't need to increase concentrations for Mo unless your pH drifts down below 5.5 and stays there.
Using a quick search I found this chart of nutrient availability pH in hydroponic systems. As you can see, 5.5 is still acceptable but on the edge. Don't worry about doing anything because you said the pH drifts back up again as it the pot dries out. It means you have some carbonates in there and they will stop the acidity from going too far. I'm still saying stick to the 0.05ppm Mo (or above) and no need to do anything else

pHhydro.JPG (52.98 KiB) Viewed 3001 times

[Steve Johnson]

Mike, I said it before and I'll say it again -- it's a genuine blessing to have you on the forum!