Dissolved urea fertilizer

14 years ago

I sowed a couple of flats with lettuce and will try raising them under lights (mostly to have something to do this time of year.)

Soil is 1/2 peat moss, 1/4 perlite, 1/4 sterile compost + 1/2 cup wood ash. Now they're up, I think I should feed them a bit of nitrogen but am not sure how much to use.

My thought is to raise the N by 0.05, i.e. go from N:P:K of X:Y:Z to X+0.05:Y:Z. I have ~20 lbs (10 kg) of (dry) soil in each flat so 0.05% is approx 5 grams of N. Since urea is half nitrogen, that would be 10 gr of urea.

So my inkling is to dissolve 10 grams of urea in enough water (1/2 gal) to evenly water the flat and water the lettuce with it.

Before I go off experimenting, I'd much appreciate a sanity scrub. A couple questions pop up:

Is the NPK calculated as a percentage of dry soil weight? I was kind of surprised just how much a thoroughly watered flat weighs compared to dry weight of the ingredients.

Is increasing N by 0.05 a reasonable amount?

I understand urea volatilizes in ~ 3-4 weeks. How often should I repeat this watering to maintain this nitrogen level? (It would seem that weekly watering with 1/3 of the urea amount would make sense, but I'm not at all sure my 'common sense makes sense' here.

I'm assuming the compost in the soil supplies enough P, and the 1/2 cup of wood ash both buffered peat acidity and supplied some K. If there's anything else I should add to these flats, I'd love to hear.

Thanks in advance.

Sort by:Oldest

Comments (3)

justaguy2
14 years ago
Before I go off experimenting, I'd much appreciate a sanity scrub.

Stand by for the 'sanity scrub' ;) (you asked for it ;) Is the NPK calculated as a percentage of dry soil weight?

No, the NPK numbers have nothing whatsoever to do with soil weight. Those numbers are based upon the weight of the fertilizer product alone. If you purchase a bag of fertilizer labeled 10-10-10 then 10% of the weight is nitrogen, 10 percent phosphorus and 10% potassium, the rest is primarily filler. Is increasing N by 0.05 a reasonable amount?

I have no idea what you mean by increasing N by .05 I'm assuming the compost in the soil supplies enough P, and the 1/2 cup of wood ash both buffered peat acidity and supplied some K.

That is a very unsafe assumption. The organic matter provides no nutrients plants can use without biological processing. Your seed starting endeavor is not likely to play host to the biological organisms needed to do the processing in a reliable manner.

I would recommend adding Miracle Grow 24-8-16 at 1/4th strength with every watering after true leaves have formed as long as you water the flats to the point you have drainage water every single time you water. If you are watering in 'sips' then you need to switch the growing media to one that allows you to water to run off every time without risk of over watering. MG 24-8-16 is mostly urea so no need to dissolve the granular fert in water and it also contains most of the other essential nutrients in a form not dependent upon biological processing to be of benefit to the plants.
josko021
Original Author
14 years ago
I do appreciate the comments - thank you. As you can tell, I'm new at this.
The reason I bring up NPK of potting soil is because I've seen it on packages of potting soil sold at my local Home Depot. The bags I looked at seem to have about 0.1:0.1:0.1 for the entire contents.
Now, if I take a bag of Bovung (1:1:1) and mix it with an equal amount (by weight or volume, I'm not sure) of sand, does it make sense to think of the resulting mixture as 0.5:0.5:0.5 ? Taking that a step further, can one think of NPK for a shovelful of garden soil? And then, what is the ideal NPK for my lettuce flat soil? Does it make sense to think of soil this way?
I use urea 'cause I can get it cheaply from a farming friend, and I've been using it for years as a lawn fertilizer. It does work there. I've got a couple hundred pounds in the basement right now, and would like to use it if it makes sense.
So maybe a much simpler question is how much urea to dissolve in a 1/2 gal of water with which to water/saturatea 18" x 18" x 4", and how often should I feed my lettuce flats this way.
Related Discussions
Urea in fertilizer ok for chinese elm?
Q
Comments (10)
Soluble fertilizers like Miracle-Gro, Peters, and many others use urea as their N source and are widely used by bonsai enthusiasts. I am quite happy using Dyna-Gro's Foliage-Pro 9-3-6 because it has all 12 essential nutrients in as close to the same NPK RATIO that plants use, and all the nutrients are present in a favorable ratio to each other. This is important from the perspective that it allows you to fertilize at the lowest rate possible and still not have nutritional deficiencies. By happenstance, the FP 9-3-6 is also urea-free. I may be getting deeper into fertilizing that you wish, so I'll offer a couple of additional thoughts & you can let me know if you want me to expand. Houseplant fertilizers are generally not a good choice for bonsai, for the reason I listed above. Most houseplant fertilizers have NPK %s like 5-10-5 or 10-15-10. The middle number is P(hosphorous) and it is usually the largest % of the whole. Plants actually use about 6X more N than P, so when you supply all that extra P in 5-10-5 it's almost 6X MORE than needed as it relates to N - after factoring for the fact that P is ACTUALLY reported as P2O5 and is ACTUALLY only 43% of the REPORTED %. What this means is you are unnecessarily contributing to the TDS/EC (roughly, the salt level) of the soil, which makes it harder for plants to take up water and the nutrients dissolved in that water. The extra P also contributes to a usually unwanted increase in pH and makes it more difficult for the plant to take up several other nutrients, mainly Fe (iron) and Mn (manganese). Many choose 1:1:1 ratio fertilizers like 20-20-20 because they say they prefer not to supply all the "extra N" that you find in 3:1:2 ratio fertilizers like 24-8-16, 12-4-8, 9-3-6 ....., but then they turn around and fertilize the plant to fill the plant's N needs. The end result is they end up supplying the same amount of N, but because the 1:1:1 ratio fertilizers supply more K and much more P than the plant requires (again, as a function of N usage) all they are doing is supplying nutrients the plant can't/won't use ..... just to get enough N. Liebig's Law of the Minimum recognizes excesses of factors with the potential to limit plant growth potentially as limiting as deficiencies. I would sum up this thought by saying you don't/can't limit the plant's N supply by changing NPK %, you limit it by limiting the actual dosage of N; or, it's dot the fertilizer that limits N supply, it's the grower. Al
...See More
Nitrogen in fertilizers and the truth about Urea
Q
Comments (33)
No worries John, I feel no hostilities from you or frostiness. Just inquiring minds want to know. I will repeat though "The source of nitrogen I think is not of great importance compared to making sure the fertilizer you use has all the micronutrients plus calcium and magnesium. The purpose of my original post was that someone should not worry about whether the fertilizer they use has urea or not." I think people look at fertilizer as a quick and easy thing that they can change and feel like they are doing something to help their plants. Things like adding more light throughout the year, increase humidity, better control of temperature, regulating ph take more effort and/or cost more. Jane is on to something when she says "The biggest change I've seen in my growing conditions would be increased light over winter. I'm getting blooms on plants I've had for years without blooms." and Jan when she says "Now to figure out how to get my city water with a pH of 9.0 to a level to make better use of all those delicious trace elements!" One thing everyone can do that is not expensive is get a water quality report from their municipal water district. This should be free. Some cities require them to be given to customers. San Francisco customers get a water report twice a year. The reports maybe online. The report will tell you things like ph, hardness, and about minerals and pollutants in the water. These can vary from spring to fall. I suspect with Jans tap water ph of 9 that her municipal water source comes from a river that flows through limestone, maybe like the Colorado. She may find she gets plenty of calcium and magnesium in her water and doesn't need it in her fertilizer. As far as nitrogen forms in fertilizers, it maybe good to cover your bet with all three as they have varying times of utilization, but I think over time it doesn't mater. I think the different nitrogen forms are present in the potting mix after each fertilizing and get used the next time, washed out, or help break down your potting medium. John to help you search for a holy grail in fertilizer you may look at these: 1 Simple sugars after all that is a big part of what the plants are making. Jerry Grow- no longer made as far as I know - exploited this. Works better in highlight and warm to hot weather. Needs more scientific study. 2. Nickel as a trace element. It is use by plants as a catalyst in urease enzyme so it is never used up, but plants grow. I have only seen one fertilizer that had nickel in it made by Hydrofarm. I have no idea if they still make it or not. I do think you can grow orchids fine with urea free fertilizer relying on ammonical nitrogen and nitrate. I will mention two things that havent been mentioned so far and are needed in the break down of nitrate to ammonia to be use by plants. Two enzymes are required. Nitrate reductase involving two electron reduction of nitrate to nitrite. The other enzyme nitrite reductase involving a six electron reduction to transform nitrite to ammonia. As you can see there are a lot more steps to get from nitrate to ammonia then with urea. Cheers, Mark Sullivan
...See More
urea as a fertilizer?
Q
Comments (6)
Yes, roses need nitrogen. But only as much as any other flowering shrub, hence why I said they don't need much. A top dressing of compost is all my roses ever get and they do great. Excess nitrogen leads to an excess of foliage growth. Which could lead to more pest and disease problems. Aphids especially love tender new growth. You want to use urea, go ahead. But as kimmsr said, it isn't considered organic and unless you want monster roses that flower sparingly you'll want to use the urea lightly. Rodney
...See More
Humic coated urea HCU is the newest fad in golf fertilizer
Q
Comments (2)
I don't know that they would really consider that as OM, more of a bio stimulant
...See More
justaguy2
14 years ago
Ah, I understand where you are coming from now. What you see on the bag is the result of CRF (controlled release fertilizer) having been added to the mix.

Trying to maintain a set amount of nutrients in the mix is going to prove close to impossible without precision testing. Using a dilute water soluble with each watering and ensuring each watering is to run off is about the closest one can come to maintaining a consistent level of nutrients in a practical sense. Now, if I take a bag of Bovung (1:1:1) and mix it with an equal amount (by weight or volume, I'm not sure) of sand, does it make sense to think of the resulting mixture as 0.5:0.5:0.5

Yes, it does, but it doesn't really mean anything when those nutrients are not immediately plant available, but instead will be released over time. To know the relative concentration of each nutrient (lets say in parts per million) would still require precision testing. And then, what is the ideal NPK for my lettuce flat soil? Does it make sense to think of soil this way?

In my opinion it only makes sense to think of it the way you are if you are doing hydroponics and have the relevant test equipment to ensure each parameter is within the specs you set. So maybe a much simpler question is how much urea to dissolve in a 1/2 gal of water with which to water/saturatea 18" x 18" x 4", and how often should I feed my lettuce flats this way.

Sorry, but I am going to have to decline to answer this as I really don't know. I am not familiar with how effectively granular urea dissolves in water. Is the product coated? If you wish to persue this approach you still need a reliable source for all other nutrients major and minor. If you wanted to do some research and math I am sure you could work it out. Look at hydro sources for recommendations in parts per million for N and then figure out the actual amount of N in your product and do the math to figure out the amount you have to add to the water to get the ppm in range.

Dissolved urea fertilizer

Comments (3)

justaguy2

josko021
Original Author

Related Discussions

justaguy2

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

Dissolved urea fertilizer

Comments (3)

justaguy2

josko021Original Author

Related Discussions

justaguy2

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

josko021
Original Author