Serious question: Urine as a nitrogen source for organic composting

For another thread, I looked up the use of urine in compost to replace nitrogen.

But I don't understand the chemistry of exactly how it all works as a compost activator and as a fertilizer.

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Do you?

After reading all the references shown below, I'm still a bit confused about how urine acts as an organic compost aid.

Here's what I can figure out so far ...

It seems while undiluted urea has an NPK of roughly 46-0-0, human urine is already vastly diluted, with an NPK of about 12:1:2. Even so, human urine must still be further diluted something like 1:10 to be applied directly to growing plants because of the chance of something called 'burning' (or 1:20 in potted plants because of salt buildup in constricted containers).

But how does it work in a compost pile?

As far as I can tell, urease in the compost soil breaks the urea molecule (NH2)2CO first into ammonium carbonate (NH4)2CO3 and then into ammonium

2NH4 and carbon dioxide (CO2 gas) & finally into ammonia molecules (NH3 gas) and water.

My main problem is what to do to make sure the nitrogen remains in the compost soil and isn't vented to the atmosphere as a gas.

Since ammonia is highly miscible in water, forming NH3(aq), I assume if I keep the compost soil moist, that will hinder venting of the nitrogen as an ammonia gas. Lower winter temperatures should also keep the ammonia more in the soil than as a gas. Apparently I can raise the pH and the amount of organic matter, which should keep some of the ammonia in the compost.

Do you have any experience in this?

REFERENCES:

- Urea:

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Reply to
Chuck Banshee
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I'd also post in rec.gardens for someone there who knows more plant biochemistry than me, but the urea in urine is no different from urea used in fertilizer. Sometimes pure ammonia is injected into soil as fertilizer and as you point out, water will hold it there.

Reply to
Frank

I switched the sci.chem to rec.gardens. Thanks for the advice.

Googling for a comparison paper of urea fertilizer and urine, I found this interesting paper from the Journal of Agricultural and Food Chemistry, 2007, 55, pages 8657-8663 titled: "Use of Human Urine Fertilizer in Cultivation of Cabbage - Impacts on Chemical, Microbial, and Flavor Quality".

Interestingly, as you intimated, they found that the urine was as good or better than the commercial stuff.

More interesting to the point, they recommended 'no more than 6 months' storage of the collected urine! I'm amazed as everything else I read said that the urine should be used within 24 hours because of ammonia (gas) formation.

I'm sure it works - but - I want to better understand the whole process so that the maximum nitrogen gets into the compost as usable nitrogen and not vented to the atmosphere as ammonia.

Reply to
Chuck Banshee

I forgot to post the URL to the scientific paper:

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I find it suspect that they found the urine-fertilized cabbage tasted 'better', as I would have expected no differences between commercially fertilized and organically fertilized (i.e., urine-fertilized) cabbage.

Still - my question is HOW best to keep the nitrogen in the compost from turning into ammonia gases and simply venting away.

Reply to
Chuck Banshee

This may help a little:

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Nothing wrong with sci.chem posting, chemist I think may comment goes to both.

Reply to
Frank

The paper purports to answer exactly what I'm asking! "The purpose of this fact sheet is to briefly describe urea transformations and to suggest how urea-N may be conserved with proper management in the field."

It says up to 90% of the nitrogen in urea will turn to ammonia gas "if not protected within a few hours of application".

Since urea -> ammonium bicarbonate (within 48 hours) -> ammonia gas, they say the key to keeping the nitrogen is to "put the urea into the soil and not merely on the soil" within those first 48 hours.

Ah. That's simple! They say you can do this three ways:

  1. Water the soil directly after applying the urea
  2. Plow the soil after fertilization
  3. Inject the urea into the soil

How did you find this? I had googled for hours before posting my question because I could not find the answer of how to keep the nitrogen IN the compost!

In my compost pile, I can keep it wet and I can cover it with soil to keep the nitrogen in the soil!

thanks!

Reply to
Chuck Banshee

Interesting question. The conversion from urea, uric acid etc to ammonia is going to be done by some microbe. I think the risk is that if you make the environment unsuitable for that class of microbes it will be unsuitable for others that are more useful. Another possibility is to try to bind the ammonia so it isn't lost as a gas. Ammonium ions ought to bind to clay and humus colloids which have significant cation exchange capacity. Also cold composting, maintaining it damp and ensuring the pH isn't too high will all reduce the loss of ammonia to the air.

I think the widespread use of urine as fertiliser is limited by lack of a suitable collection mechanisms and the yuck factor. The latter is composed of the reaction to the smell and the belief that it is "dirty". The yuck factor is a big issue. People are often aghast at the idea of water derived from treated sewerage being used in the normal water reticulation system, despite evidence that the water would be as safe or safer than collected ground water.

The smell issue is commonly accepted as not a show stopper when using manures. Poultry manure or poultry bedding which contains large amounts of manure can produce a most revolting stench far worse than human urine but this doesn't stop them being used at least in agricultural settings. If I lived in a built-up area I would be restricted in using such fertilisers due to having regard for neighbours.

If you ask Mr or Ms Public is urine safe to use on the garden they will probably tell you that you can catch diseases from it. This isn't true in general. It may possibly be true if the donor has a urinary tract infection, such a person would very probably be aware of the illness and so should cease donating until they are well. In the absence of such an infection fresh urine in sterile. It could also become infected if stored in such a way that it became a growth medium for microbes that originated elsewhere. If you are adding it to your compost or even directly to the soil this is hardly likely to be an issue. As the article points out the few pathogens found cannot easily get into the cabbages. Bring up your kids to pee on the lemon tree!

As the price of oil (and so synthetic nitrogenous fertilisers) goes up we may find some creative person who can find a way to collect urine cheaply instead of sending it down our rivers and out to sea and then having to use power to fix atmospheric nitrogen in its place.

David

Reply to
David Hare-Scott

Or wash it away into aquifers, or public water ways. The amount of ammonia needed to produce the same yield from a field will increase as the organic material (OG) in the field's soil breaks down and diminishes. Discing OG into the field disrupts the soil structure and ecology.

With urea, you needn't spare its application, as you have a lifetime supply of it. Do spread it around though, as you can get salt (ionic compounds that result from the neutralization reaction of an acid and a base) build ups if it only supplied to one small area of soil.

The Bottom Line ? Ideal soils, from a fertility standpoint, are generally defined as containing no more than 5% OM by weight or 10% by volume

? Before you add organic amendments to your garden, have your soil tested to determine its OM content and nutrient levels

? Be conservative with organic amendments; add only what is necessary to correct deficiencies and maintain OM at ideal levels

? Do not incorporate organic amendments into landscapes destined for permanent installations; top dress with mulch instead

? Abnormally high levels of nutrients can have negative effects on plant and soil health

? Any nutrients not immediately utilized by microbes or plants contribute to non-point source pollution

Reply to
Billy

If the ratio of brown to green additives to your compost pile is about

25/1, you pile won't smell as it will be in balance with the needs of the composting microorganisms. Then the urea will be bound in the proteins of the flora and fauna of the soil ecology, and will be released at a use able rate for the plants during the microorganisms' life/death cycles. To insure the minimum lost of nitrogen, cover its source with mulch that is kept damp, i.e. compost in situe.
Reply to
Billy

Did you know that during the Civil War, Southern women would save their urine to use for explosives?

Reply to
micky

In olden times it was the source of saltpeter to make gunpowder:

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Reply to
Frank

It's uncalled for to attack someone's unsubstantiated theory as 'dumb billgoat' as there may be a basis in fact to the original statement ...

However, in this thread, we're only looking for scientifically proven data for preventing the nitrogen in urea from gassing off as ammonia.

So, while I won't believe the 25:1 ratio above until/unless scientific evidence shows it to be be true, I 'can' believe what was implied in the following references:

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Basically, these documents tell us from 50% to 90% of the nitrogen in urea is lost to the atmosphere (as ammonia) when urine is simply poured on top of the compost pile and left there.

The reason is that some of the urea [(NH2)2CO] is first turned to ammonium carbonate [(NH4)2CO3] and then into ammonium [2NH4] and gaseous carbon dioxide [(CO2 gas)] & finally into gaseous ammonia [(NH3] and water [H2O].

The goal is to force that nitrogen that would otherwise gas off, to recombine into compounds (nitrates?) that plants can use. I haven't figured out 'what' compounds these would be - so if you have papers on that, it would be useful to know.

So far, to minimize the nitrogen gassing, I will employ two techniques:

- I'll maintain the moistness of the compost heap (by sprinkling water)

- I'll cover the heap in clean soil (as I do anyway to deter vermin)

If anyone finds a BETTER way to forestall nitrogen evaporation in urea- enhanced composting, please cite how (references are always appreciated!).

And, if you know WHAT the process is that converts the nitrogen to useful compounds for the plants, I'd like to know also.

Thanks all!

Reply to
Chuck Banshee

Drink more water, pee more often.

Reply to
croy

Urine has a fertilizer value of N/P/K 18:2:5. Wow!

Plant Physiology

Nitrogen assimilation and fixation

Availability of nitrogen to plants is often a limiting factor in growth and productivity ? despite the fact that N2 is the most abundant gas in the atmosphere Nitrogen can exist in pools of different chemical forms, nitrogen cycle

? reduction of N2 to ammonia=nitrogen fixation (bacteria, lightning, industrial)

? ammonia is oxidized to nitrite, then nitrate=nitrification (by some bacteria)

? organics are converted to ammonia=ammonification (by bacteria & fungi)

? nitrate is reduced to N2, returned to the atmosphere=denitrification (bacteria) In taking up and utilizing nitrogen, plants incorporate it into carbon-nitrogen compounds Most plants take up nitrogen primarily in the form of nitrate (NO3-)

? except in conditions where nitrifying bacteria don't grow well (low pH, anaerobic)

? then ammonia (NH4+) will be available for uptake

? many forest species take up primarily NH4+, since forest soils are more acidic (less nitrification)

? NH4+ leaches less than NO3-, since NH4+ adheres to soil colloids NO3- is actively transported into and concentrated in the cells by a NO3- / H+ carrier (symporter) Assimilation: NO3- is reduced to nitrite (NO2-) by nitrate reductase using NADH ? addition of NO3- induces the expression of nitrate reductase (regulated at transcription and enzyme activity)

? nitrate reductase has Mo, heme, and FAD cofactors (Mo deficiency can lead to N deficiency) NO2- is reduced to ammonium (NH4+) by nitrite reductase using ferredoxin (Fd)

? nitrite reductase has Fe-S and heme cofactors

? located in plastids NH4+ is incorporated into carbon compounds: amides (amino acids) and ureides Incorporation into amino acids is primarily by the GS-GOGAT pathway GS-GOGAT cycle

2 glutamate + 2 NH4+ + 2 ATP -> 2 glutamine + 2 ADP ? enzyme is glutamine synthetase (GS) glutamine + alpha ketoglutarate + NAD(P)H -> 2 glutamate + NAD(P)+

? enzyme is glutamate synthase (GOGAT)

Reply to
Billy

Now that's interesting!

Since it's compost we're working with, we don't know (yet) which plants will be using the nitrogen.

So, I guess, we want the nitrogen as both a nitrate (NO3-) and as an ammonia (NH4+).

I wonder how we know if a plant that we plan on fertilizing with this compost uses its nitrogen as nitrates versus ammonia?

And, depending if we want more nitrates versus more ammonia, I wonder what we'd need to do to tilt the chemical balance one way or the other?

Reply to
Chuck Banshee

Don't know if the ways to reduce N losses are "better" rather than just different.

Diluttion, watering in & cultivation are mentioned along with some chemical techniques.

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cheers Bob

Reply to
DD_BobK

I don't think it is feasible to manage the situation down to that level of detail in soil.

David

Reply to
David Hare-Scott

Nice one. Lots of good numbers to use as a reference point.

I liked the section on how to minimize nitrogen losses in stored & applied urine via non-ionized ammonia gassing.

"The urine mixture should be quickly incorporated into the soil, to minimize ammonia loss. The best method of doing this is by applying urine to farrows or holes, which have to be covered over immediately after application."

For storage, they suggested reducing the pH from 9 to 3 using a fertilizer-friendly acid (e.g., by adding 26 mmol of sulfuric acid (H2SO4) per liter of urine.

They said one study never lost more than 10% of the nitrogen (as non- ionized ammonia gas) during application - but that once applied and protected by a cover of soil, further nitrogen losses, they say, were "negligible".

And, their estimation of about 5 grams of nitrogen per liter of urine, and of 500 liters of urine (which is five pounds of nitrogen) and 50 liters of faeces per person per year may be useful overall, as a background metric. (They estimated a single person's urinary nitrogen/ phosphorous/potassium output was 2.4kg/0.3kg/1.1kg per year.)

In addition, I hadn't realized urine composting reduces carbon emissions, especially since it does release carbon dioxide as a gas, in addition to ammonia gas.

I also hadn't realized we excrete exactly the same amount of nutrients that we eat (I would have thought some was consumed somehow), and that the amount of NPK excreted in urine was roughly 90% for Nitrogen, and about 75% (roughly) for both phosphorous & potassium.

I'll add it to the reference list:

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Reply to
Chuck Banshee

It is a peculiarly American obsession with balancing compost heaps though. You *really* have to work at it to get a compost heap not to behave correctly if you are adding a cubic metre or so of stuff at a time. The whole heap goes hot and rots down fast no matter what you put on. Woody thick stems do need mixing in with something nitrogen rich - but grass cuttings will do the job just as well as anything else.

A hot heap with a lot of grass cuttings on *will* smell of short chain fatty acids during the fast stage breakdown - slightly sweet stale BO smell for a few days. And one of mostly pine needles and trimmed conifer branches will smell of oil of wintergreen. You can get it to smouldering internally in a big heap. Provided that you don't crush the air out of it you can get fast composting this way with almost any mixture of materials added. You might at the start of a season need to feed it with a starter culture - particularly for a small garden.

If you manage to make it anaerobic wet and slimy then you will get a reducing environment and ammonia gas emitted, but otherwise the fungi and bacteria can pretty much look after themselves and turn your urea into bound ammonium salts. There will always be a slight smell during compsoting so you don't want the heaps too near the house!

The main one is make sure the heap stays suitably moist (not wet) and hot. This means a heap size and shape that is roughly cubic. Ammonia is very soluble and if there are short chain fatty acids around from the decomposition of other material it will be bound as ammonium salts.

In the early stages of composting any free ammonia should react with some of the otherwise volatile short chain fatty acids. Both will smell if they escape from the pile.

Not worth the effort of covering it with soil. The thin top layer tends to dry out and will need turning over but it gets burried next time you cut the grass anyway.

Oxidation to soluble nitrates and combining with short chain fatty acids as slightly more stable ammonium salts.

Regards, Martin Brown

Reply to
Martin Brown

As the article says, the reaction is driven by the pH; High pH --> NO3-, Low pH --> NH4+

In general, annuals like high pH, and perennials like low pH.

Another wrinkle that I haven't investigated much is mycorrhiza. A symbiotic (generally mutualistic, but occasionally weakly pathogenic) association between a fungus and the roots of a vascular plant.

Reply to
Billy

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