Fertilizer question

[consettbay2003]

How stable is a fertilizer solution that contains ureic and ammoniacal nitrogen?

 

[Rick]

under sterile conditions and low/neutral pH it could sit around for weeks.

But once a little bacteria or algae get going it falls apart pretty quick.

 

[consettbay2003]

Would the 'falling apart' be reflected in a change in the EC of the solution?

 

[Stone]

Would the 'falling apart' be reflected in a change in the EC of the solution?

Urea does not register on a salinity meter as it does not form ions, however it quickly (2 days ) gets converted to Ammonium which will increase EC reading.
Rick might be able to answer this properly but I believe under certain situations (temp/pH?) some can be lost as gas (ammonia)

 

[Rick]

Ammonia doesn't gas off very well until the pH gets up past 8.5.

The urea pretty much gets split in ammonia.

I wouldn't really expect to see a substantial drop in conductivity as long as the pH is maybe under ~~7.5ish. If you are seeing a lot of solids development, it could be bacteria growth (plain old removing N from solution into biomass or converting to N2 gas if the system goes septic), or maybe Ca or Mg solid formation (you didn't say what else is in the formulation). With the formation of solids you might see a significant drop in conductivity.

 

[consettbay2003]

Follow up question

Does the fact that urea does not form ions mean that my initial Ph reading like the initial EC reading will be inaccurate? Will the Ph reading also change over time (i.e. one week)?

 

[Rick]

I can see the pH changing over time. Especially if biology happens in the mix.

Depends on how much oxygen is in the system. Under aerobic conditions, I would expect the pH to drop. Under low/no O2, the pH will actually increase.

What could also happen is first the pH drops as N is utilized (sucking up the bicarbonate and DO) by the nitrifiers. Then once the aerobic bugs suck up all the DO, then the anaerobes kick in and start making alkalinity, driving the pH back up.

How long do you want it to last?

Maybe you can ultra filter it, and keep it in the fridge if it needs to hold up for weeks/months.

 

[consettbay2003]

My plan is to alternate using Akerne's Rain Mix (13-3-15 with 11CaO + 3MgO) at 1/4 tsp./gallon in RO water, with a mixture of equal parts calcium nitrate, magnesium sulphate, and Miracle Gro (20.5% Ureic and 3.5% ammoniacal nitrogen) at 1/8 tsp. each per gallon of RO water.
In between fertilizer applications I flush with RO water to which I add 1/8 tsp. of both calcium nitrate and magnesium sulphate.
Suggestions?

 

[Rick]

That seems like an awful lot of food and complication.

I think you would do fine with weekly feedings at 1/8 or 1/4 each of a mix of the Akerne's, cal nitrate, and mag sulfate (is this Epsom or anhydrous MgSO4? If its Epsom you need to double the amount since its 50% water by weight already)

Since you have RO water, instead of mixing nitrate and sulfate salts into it, just add back enough tap or well water to run the hardness up to about 20ppm.

You don't need to get so crazy with nitrogen.

Does Akerne's have the matching "well water" mix like MSU? If you feel you just need more ammonia than the rain water mix, then switch to the mix for higher alkalinity.

What is the hardness alkalinity and conductivity of your household water? That's a faster/cheaper way of getting calcium/magnesium/bicarb and sulfate into your plants. Give me those numbers and we can design a simple work around easy enough.

 

[consettbay2003]

I recall reading ( Antec site? ) that the calcium and magnesium in tap water is not as readily available ( and disolvable ) as calcium nitrate and magnesium sulphate.

The magnesium supplementation I use is Epsom Salts. The box says Magnesium Sulphate but the analysis indicates:

Magnesium Oxide (MgO).
soluble in water 16.5% (10% Mg)

Do you feel that 1/8 tsp Akerne's Rain Mix (EU MSU substitute), 1/8 tsp. Calcium Nitrate and 1/8 tsp. of the above Epsom Salts per gallon would be a good combination?

Some of my paphs. need watering every three days so I would feel more comfortable with in between waterings of RO with Ca and Mg supplementation.

 

[Rick]

I recall reading ( Antec site? ) that the calcium and magnesium in tap water is not as readily available ( and disolvable ) as calcium nitrate and magnesium sulphate.

The magnesium supplementation I use is Epsom Salts. The box says Magnesium Sulphate but the analysis indicates:

Do you feel that 1/8 tsp Akerne's Rain Mix (EU MSU substitute), 1/8 tsp. Calcium Nitrate and 1/8 tsp. of the above Epsom Salts per gallon would be a good combination?

Some of my paphs. need watering every three days so I would feel more comfortable with in between waterings of RO with Ca and Mg supplementation.

Unless you see white chunks floating in your tap water all the Ca and Mg is fully dissolved. I don't understand the Antec comment at all, and doesn't make sense.

Epsom salt is the hydrated form of Magnesium sulfate, so you will need to use twice as much as the anhydrous form to get the same effect. So 1/8, 1/8, 1/4 tsp/gal.

Can you get the hardness, alkalinity and conductivity values for your tap water? Hardness is the amount of soluble calcium and magnesium in your water. So very important to figure out how much is good to dilute with your RO.

 

[consettbay2003]

Sorry but this is not my field of expertise ( I'm not sure I have one! ) so please excuse any 'stupid' questions.

If the Epsom Salts I am using is actually MgO as the box indicates, why is it called Magnesium Sulphate on the label and not Magnesium Oxide and will the plants be getting sufficient sulphur as none is listed in the chemical composition on the label? The magnesium in the Akerne's Rain Mix is also MgO.

 

[DavidCampen]

Sorry but this is not my field of expertise ( I'm not sure I have one! ) so please excuse any 'stupid' questions.

If the Epsom Salts I am using is actually MgO as the box indicates, why is it called Magnesium Sulphate on the label and not Magnesium Oxide and will the plants be getting sufficient sulphur as none is listed in the chemical composition on the label? The magnesium in the Akerne's Rain Mix is also MgO.

If the label says "Epsom Salts" then it is magnesium sulfate which is water soluble and supplies sulfate as well as magnesium ions. For whatever reason, the label analysis considers only the magnesium content to be important and also has decided to report the magnesium content as magnesium oxide (much like the potassium content of fertilizers is reported a potassium oxide). Is this in the US? I have never actually looked at the analysis on a label of Epsom Salts.

As for the Akerne's product I have no idea but I would expect the magnesium to be in a soluble form though it may not have been the sulfate so you will not be able to infer anything about the sulfate content.

 

[Rick]

It might be an agriculture convention used rather than US or EU.

For some reason the agri types like to put things in terms of the oxides of different cations rather than the chemical formula that chemists will use.

When I pick up epsom salt at the drug store, it is written up as MgSO4 on the label here.

But just my guess.