MSU fertilizer PPM scale

[keithrs]

I was wondering what scale(500/700) MSU used to calculate 125 PPM?

[Ray]

I'm not sure what you mean exactly, but for ANY fertilizer, for 125 ppm N (not 125 ppm TDS):

10 / %N = teaspoons per gallon

13 / %N = ml/liter

[keithrs]

So, Why do they calculate just PPM's of N? Every other fertilize company uses EC to calculate PPM.

[Ray]

It is common for professional nurserymen to manage their feeding regimen by controlling the nitrogen application, as that has the most impact on growth, while "tuning" the remaining nutrients via their selection of specific formulas.

The classic example is poinsettias - it is well established that it takes 1/2 g N to raise the rooted cuttings to maturation and blooming. If you are raising them in different substrates - soil, peat-based, coir-based, etc. - you still need the same amount of nitrogen, but will change the rest of the formula to accommodate the substrate. The EC of each will be different for the same nitrogen loading.

The Greencare folks provide EC as well, for a target nitrogen loading. I think that is how it is specified on most professional fertilizers, not EC for a total dissolved solids level.

MSU RO (ppm N-mS)
50-0.4, 100-0.8, 150-1.0, 200-1.6

MSU WW
50-0.34, 100-0.68, 150-1.02, 200-1.34

[keithrs]

Thanks for the explanation!

To get 125 PPM N for MSU, your TDS is about 450-630.... depending on the scale?

So, Im guessing that the hydroponic world is alittle different than. Being that they can add up to 5 or more different products in the tank at one time.

So.... When your plants go into blooming cycle do you want to measure PPM's of P?

[Ray]

At a constant nitrogen concentration, the TDS will vary with each different formula, but will be constant, and I don't know the number.

Look at it this way: if you total up the cations in all of the minerals and chemical used to make up the Greencare MSU RO formula, the TDS would be 355. However, we know that the anions play some role in the dissolved solids, but how much?

If we take the total mass or powder added - again for 125 ppm N - that's 3.55g in a gallon, or 3550mg/3.785kg = 938 ppm, but depending upon how the particular species in solution dissociate, some of them are not part of the TDS either, so it's probably somewhere in between.

If we switch to the Well Water version, those numbers are 263 ppm and 661 ppm, respectively.

Why would you want to measure the phosphorus? A plant has little demand for it to start with, and that does not change in relation to blooming.

[keithrs]

I not wanting to measure phosphorus...... I'm no chemist nor botanist, But it just make sense to me that if you measure N for the growth cycle since thats what's responsible for growth, you would want to measure P when your plant is about to go into bloom cycle and lowwer the PPM of N.... It's my understanding that P is a major player in bloom. Again, I'm probably all wrong about this but Im ok with that.... That how you learn.

[DavidCampen]

Originally Posted by Ray

, ... but for ANY fertilizer, for 125 ppm N (not 125 ppm TDS):

How and by whom was the value of 125 ppm of nitrogen determined? Why not a value of 100 ppm or 150 ppm?

Edit:
This is intended as a rhetorical question because some people here seem to have become fixated on this value of 125 ppm nitrogen as some inflexible requirement instead of just a quick rule of thumb. And in fact you mention here ( TDS and EC ) that 125 ppm is just a value that you "typically shoot for".

If we take the total mass or powder added - again for 125 ppm N - that's 3.55g in a gallon, or 3550mg/3.785kg = 938 ppm, but depending upon how the particular species in solution dissociate, some of them are not part of the TDS either, so it's probably somewhere in between.

If you dissolve 3.55 grams of material in a gallon of RO water then the TDS _is_ actually (by your calculation) 938 ppm. The only thing approximate (as you mention here: TDS and EC ) is what reading will be obtained from an EC meter that is being used to estimate the TDS.

If I dissolve 3.55 grams of sugar in a gallon of RO water then an EC meter will give a TDS reading of 0 even though the actual TDS is 938 ppm.

And, actually, what is really important is the osmolarity of the nutrient solution which is yet another topic.

[Ray]

Originally Posted by DavidCampen

How and by whom was the value of 125 ppm of nitrogen determined? Why not a value of 100 ppm or 150 ppm?

There is absolutely nothing "magic" about 125 ppm N, at all.

The number is the one that the folks who developed the so-called "MSU Fertilizers" decided to use when evaluated their formulas, and found it worked well for their varied collection of orchid genera. (Coincidentally, I happened to have discussed that with Bill Argo, on of those developers, just last week.) One of them simply suggested it, and they went with it.

It seems to be a reasonable level to apply frequently without fear of "burning".

[orchids3]

Ray,
Thanks for your explanation - but this guy seems to believe that Phosphorus has something to do with blooming. Not unusual but a chance to get on the soap box if you are anything but a fertilizer salesman.