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What is in urine?

Glass of peeSince we're considering using urine as a fertilizer, it makes sense to figure out what's in that yellow liquid.  The actual percentages of each component can vary depending on what you eat, but pee from an average Westerner has an NPK of 11-1-2.5.  For those of you not familiar with NPK, that's a fertilizer that's very high in nitrogen, low in phosphorus, and moderate in potassium.

After water, the major components in urine are high nitrogen chemicals including urea, creatine, ammonia, and uric acid.  Pee also contains a significant amount of salt (sodium chloride), and a bit of calcium, magnesium, and sulfur.  Rarely will urine contain a few disease-causing organisms --- primarily leptospirosis and schistosoma in the tropics, and salmonella (which dies quickly in soil.)

Beyond the unbalanced NPK (which can be fixed by mixing the urine with other nutrient sources, like chicken manure to increase the phosphorus and wood ashes to increase the potassium), the primary problem with using urine as fertilizer is salt.  If you fertilize solely with urine, your soil may build up salts to a level which harm the plants growing there, so Carol Steinfeld recommends using urine as fertilizer only in regions with regular rainfall to wash salt away.  A high tech option consists of buying a Total Dissolved Solids (TDS) meter from a hydroponics store to monitor salt content of your urine, then diluting the urine down Fertilizing a garden with reduced-salt urineto 1,700 ppm salt before using it as fertilizer.  Alternatively, just spread urine around a lot, never focusing on one part of the garden, and salt buildup will probably be minimal.  Finally, a doctor-gardener profiled in Liquid Gold (and pictured here) took a more proactive approach --- he put himself on a low-salt diet so that his plants wouldn't be hindered by the salty urine.

I wasn't entirely content with Carol Steinfeld's answers about salty soil, so I did a little research of my own.  Although extension service and USDA websites don't talk about applying urine to your plants, they do have answers for salt buildups from other sources.  Reading between the lines, I would suggest applying your urine to salt-tolerant crops such as asparagus and zucchini, while steering clear of salt-haters like beans, carrots, okra, onions, parsnips, peas, and strawberries.  Don't apply urine to waterlogged or high clay soil since these soils will hold onto the salt no matter what you do --- sounds like we should keep our urine out of the badly-drained back garden.  If you're concerned that Pots of plants fertilized with urineyou've overdone it, you could send your soil in to be tested by the experts, or you can follow the Colorado State University Extension's lead and use bean plants as biological indicators: "Bean plants are rather salt sensitive and can be used to help assess salt problems.  In a garden, if beans are doing well, soluble salts are not a problem."  The cure for salty soil is adding lots of water (6 to 24 inches in a slow, continuous stream) to leach the salts out.

As long as you understand how to prevent salt buildup in the soil, it sounds like urine is a great fertilizer.  Liquid Gold's website includes some beautiful pictures from gardeners who fertilize with urine, and we're keen to work the kinks out of applying urine to our own farm.  Stay tuned for tomorrow's post about the nitty-gritty of urine fertilizing.

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This post is part of our Urine Fertilizer lunchtime series.  Read all of the entries:

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Given the amount of space you have, and the amount of urine that two people can produce, will salt ever really be a problem?

How much urine would you have to apply per square foot (or whatever) to cause a problem?

Comment by Darren (Green Change) Wed Jan 19 16:56:38 2011
I suspect you're right in your guess, but I'd really love to see real data on the issue! Unfortunately, I haven't found answer to your second question anywhere --- if someone else finds it, I would be thrilled. I'd also really like to know where all that salt goes. I assume it filters down into the subsoil --- could the subsoil become toxic to deep-rooted plants as a result?
Comment by anna Wed Jan 19 17:25:46 2011

Seeing how well salt dissolves in water and given the fact the osmotic pressure will tend to spread out the salt through the water table, I think you'd need a lot.

Along the Dutch coast infiltration of seawater is a problem due to the low water levels in our reclaimed land. But there is a lot of salt in seawater.

As an experiment, take a glass of water and add salt until no more salt will dissolve. Now take a small sip to get an impression of how much salt that really is... I can guarantee you that you'll spit it out immediately! (You'll want to rinse your mouth with fresh water afterwards) :-)

How much salt will accumulate will depend a lot on drainage of the land, permeability of the soil, rain, sunshine etc.

Comment by Roland_Smith Wed Jan 19 18:18:47 2011
If the urine in that glass is from one of you, that person needs to drink a great deal more water. If a person drinks lots of water the urine will be almost clear, not yellow. I am not sure what makes the urine yellow as show, but after reading what you wrote, I am wondering if it is a build up of salt in the body, as well as other things.
Comment by Sheila Wed Jan 19 21:14:46 2011

There must be something weird about my interests, when the topic of using human urine as fertiliser comes up twice in one day in my RSS feeds!

Comment by dar Wed Jan 19 21:48:27 2011

Roland --- I knew I could count on you to chime in. :-) I think that plants can probably "taste" salt at a much lower percentage than the one you've mentioned, though. What I don't know is what percent salt will harm plants --- I guess that would be where to start my research, huh?

Sheila --- I stole that photo off the internet, and I think it actually is probably food coloring. I agree that healthy urine shouldn't look nearly that yellow. The internet says that yellow urine is caused by urobilins, which is a broken down product of bilirubin, which in turn is a broken down product of used up hemoglobin.

Darren --- What's weird about urine as fertilizer? :-) (I've got Gene Logsdon on my RSS feed --- I'll have to go see what he has to say today.)

Comment by anna Thu Jan 20 07:56:29 2011
urine color is dramatically affected by what you eat. my prenatals have HUGE amounts of betacarateen (sp?) in them so my urine tends to be even darker than that, with an almost neon yellow color. if I forget to take them for a day the urine is almost clear, so I know it is not dehydration.
Comment by Anonymous Sat Jan 22 13:02:12 2011
The author of Liquid Gold is always careful to mention that the values she gives you are for the typical Western diet. I suspect that all of the components of urine --- not just the color --- could vary drastically depending on what you eat.
Comment by anna Sat Jan 22 15:19:07 2011
You all are talking about yellow urine.Urine is suppose to be clear.If you drink alcohol it gets very yellow.Whiskey im talking about.Now would that type of urine be bad for the garden.Also,your talking about community urine shared.Would if someone in your community had aids,hepatitus or something of the sort.Wouldnt that go back into the veggie your growing.That would kinda worry me.
Comment by Dawn Sat Feb 11 04:20:28 2012

Dawn --- Even if you're well hydrated and healthy, I don't think your urine would ever be completely clear --- just a lot paler.

I don't know much about alcohol, but my vague understanding is that it tends to dehydrate you. That would make your urine much yellower, as you mention.

I haven't personally looked into every possible illness, but there have been lots of scientific studies of using urine on food-growinggardens, especially in places like Sweden where they do it on a large scale. The idea is that diseases that survive well in our bodies can't live in the completely different conditions of the soil. Beneficial soil microorganisms outcompete them very quickly. So, if you use urine on your tomato plants, then wait at least a week, any pathogens are going to be long gone.

Comment by anna Sat Feb 11 08:23:23 2012

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