Urea Nitrogen Al's 5-1-1?

TheMasterGardener1(5B)October 25, 2011

Hi. Im sure this has been asked time after time. Will MG fertilizer work in the soiless 5-1-1? Will the urea break down into usable form in soiless? I know FP is ideal because it has nitrate N and no urea N. Will MG that has urea in it work?


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MG should be fine, from what I've read here--FP is ideal for convenience, but MG can be used as long as you supplement missing micronutrients.

If you do a forum search for "5-1-1 urea" you may find some relevant threads--I saw one where Al was discussing specifics on using a urea fertilizer.

The main requirement AFAIK is that it be an immediately available, soluble source of N, and I believe MG fits that bill.

(Anyone feel free to correct me if I'm wrong here!)

    Bookmark   October 26, 2011 at 1:48AM
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tapla (mid-MI z5b-6a)

Lol - you're gonna make me THINK! ;-)

Urea is soluble in water, and MG fertilizers are a good choice for use on containerized plants, as long as the NPK formulation is appropriate. Dissolved in water, urea itself is neither acidic or basic, but it does produce an acid forming reaction as it is taken up by plants. I'll explain:

There are three types of nitrogen used in water-soluble fertilizers: ammoniacal nitrogen (NH4-N), nitrate-nitrogen (NO3-N) and urea.

Ammoniacal nitrogen is acidic (file a mental reminder that that both words begin with "A" - acidic and ammoniacal). When ammoniacal nitrogen is taken up by roots, roots secrete acidic H+ into the soil. The more H+ in the media, the lower the media pH. Urea is easily converted into ammonium in the soil and should therefore be thought of as an acidic source of N.

In contrast, uptake of N from nitrate (NO3) sources increases substrate pH because basic OH- or HCO3- are secreted by plant roots into the root media when NO3 is taken up. Since OH- and HCO3- are bases, NO3 uptake tends to cause the media-pH to increase.

MG gets all of it's N from urea, while FP utilizes ammoniacal forms of N for a little less than 1/3 of its N, the rest comes from NO3 sources. This is an advantage in low light situations because NO3 forms of N tend to produce plants with shorter internodes and thicker stems/branches - bushier plants. FP also contains Ca(lcium) and Mg (magnesium) in soluble form, elements usually missing from most soluble synthetic fertilizers. This CAN be an advantage when growing in certain soils (like the gritty mix), but isn't much of a consideration when growing in soils pH adjusted with and getting Ca/Mg supplied with dolomitic lime - the most common source of Ca/Mg.


    Bookmark   October 26, 2011 at 10:46AM
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hex, Thank you alot. That is good to know, now im set then.

Al, Thanks for your time. I have learned alot from reading your discussions. If I supply lime=Ca/Mg, the only thing missing from the micro is sulfur, is that needed?

Otherwise, looks like I'm good to go for this coming spring. I am going all in containers using the 5-1-1, no more peat! When I make the 5-1-1 I can see it is the best media ever!

Thanks again.

    Bookmark   October 26, 2011 at 6:16PM
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I have had an excellent year using 5-1-1 with MG. I used the dolomitic lime for the mix, but didn't use it after. I have used some epsom salts with it, but haven't had to add any Ca, and have had no Ca deficiency symptoms. I mostly water with rainwater, but occasionally use tap water when the barrels run dry, which likely adds to the Ca. I had a bumper crop of peppers with this combination with no sign of any deficiency.

    Bookmark   October 27, 2011 at 1:17PM
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Thanks alot!

    Bookmark   November 1, 2011 at 2:23AM
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