Urine is a "complete" fertilizer in that it has a wide range of nutrients including the major nutrients that plants need: nitrogen, phosphorus and potassium; secondary nutrients such as calcium, magnesium and sulfur; and micronutrients (which plants need in much smaller amounts). Here's the breakdown for aged urine (fresh urine has more phosphorus and magnesium, some of which precipitates out as struvite during storage):

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Like r/unworthythor’s slug question, this isn’t something we’ve researched ourselves (or have found scientific studies of) but the bonus-use for deer-deterrence (and possibly woodchucks as well) is something we hear quite often through our community science program as well! Some people even recommend pouring urine around the perimeter of the garden to discourage animals from entering, such as along the fence (this may kill any plants living in that perimeter due to over-application of nitrogen). It is also important to repeat the application following rain.

We don't mind sharing! Responses from the three of us here today:

Abe - In college (at College of the Atlantic, in Maine) I studied ecology, and I became fascinated with nutrient cycles–specifically the cycling of nutrients through farmland and then our bodies. When I learned that most of the nutrients in the food we eat leave our bodies in our urine, it seemed like such an elegant solution to recycle them back into agriculture. My garden agreed that this was a good idea, and I was inspired to work on researching and demonstrating this strategy at the home, community, and farm scales. Yes, people really like to talk about at parties! This surprised me at first, but I think people are fascinated that a thing they make and throw away every day can actually be part of a beneficial cycle.

Tatiana - I got into this when I was working as a journalist and interviewed Abe Noe-Hays about "peak phosphorus" - I was doing a story on this, and had heard about Abe and Rich Earth's work with urine recycling. It just made sense to me that rather than flushing our urine down the toilet (and mixing with potable water) we should reclaim that urine - at the time I was focused on the phosphorus content, although as far as fertilizers go, the nitrogen content is usually emphasized since urine is a high-nitrogen source.  After learning more about it, I became enthusiastic enough to join the board of Rich Earth, and later, when Rich Earth received a grant from the National Science Foundation, I was hired on staff due to my background in environmental anthropology (Antioch New England grad school)  - i.e. the relationship between people and the natural world. I am interested in how people think about their connection to nature, and what we do with our "waste" fits into that bigger picture. I'm intrigued that as people become more comfortable with urine recycling, they also often seem to re-think how we fit into ecosystems and our habitat.

Julia - I had been studying the effects of our conventional wastewater systems - including combined sewer overflows, and their environmental injustice implications -  and generally learning about how ill-equipped our conventional systems are to meeting the new stresses of climate change. I was really interested in learning about who was advancing alternatives, and came across the Rich Earth Institute through Vermont’s ECO AmeriCorps program (a great way to spend 11 months with us for any early career folks out there!) The abundance of pee-puns is also a perk of the job. And the hopefulness! While a lot of the environmental sphere can feel disheartening, this is an area where a lot of new connections and lightbulb moments are formed when we explore how reclaiming our ‘waste’ can fertilize social change. Together we can pee the change! 😉

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However, if you have a high carbon content compost heap (mostly straw, dead leaves, sawdust, or other dry, dead plant material), then it will retain the nitrogen in urine fertilizer - and the urine can actually help accelerate the composting process. You can read a past research project we did on urine fertilizer and compost here. Our colleagues at Compost For Good have also done trials on in-vessel composting with urine which you can watch on our 2023 Summit website under Urine Treatment and Processing Research Part 1.

Adding urine to compost risks losing some of the nitrogen to the atmosphere through ammonia volatilization. Also, urine adds a lot of nitrogen and moisture, and it can be easy to add more than the pile can use--especially if the other ingredients have significant nitrogen or moisture already (such as "green" items like lawn clippings.) Whether it is "necessary" depends on how you are using the fertilizer, as noted in the previous response - it's more rapidly absorbed by plants when applied directly rather than adding to compost. As for safety, pure urine (without any fecal contamination) is safe to use in home gardening without composting or other treatment, provided the gardener follows the guidelines in World Health Organization’s “Guidelines for the safe use of wastewater, excreta and greywater - Volume 4“ pages 70-71. These guidelines include washing hands after handling urine, and waiting for 30 days after fertilization before harvesting produce to be eaten raw. Hot composting would provide a secondary safety measure, but is not necessary for health protection. Adding urine to compost poses no additional health concerns compared to using it directly.

Right - it is very low because of the high water content.

😂 We hear your struggle! The regulatory landscape in the US for home installations of onsite reuse systems is quite challenging, and often requires a redundant septic system/leach field anyway. Some contacts who can help with the permitting-pathfinding and installation process if you do decide to pursue something more permanent:

• Nutrient Networks
• Point of Shift

We also run a EcoSan Permitting Group with our collaborator Mathew Lippincott (listserv & bi-monthly state-state support meetings) that anyone is welcome to join!

As long as the urine is in a closed container, there should not be any nitrogen losses. We conducted a study on application methods for farmers, to reduce ammonia volatilization, which may be of interest. The results are here.

Great question! Pharmaceutical compounds do come out in urine. We actually conducted six years of research in partnership with the University of Michigan focusing on this question specifically. You can learn more about this research on our results webpage.

Basically, when we flush our pee, drug compounds accumulate downstream with negative ecological effects that ramify up the food chain. When we reclaim our urine as fertilizer, those compounds are given a chance to be broken down in the soil and don't accumulate in crop tissue at a significant level. 

We tested 20 different pharmaceuticals and 2 metabolites. In the final year of research, we also added 3 natural hormones (estrone, estradiol, and estriol), and one synthetic hormone (ethinylestradiol), for a total of 26 different compounds. These pharmaceuticals and metabolites were chosen to represent a diversity of types of medication as well as a variety of chemical properties. The amounts and concentrations used were based on the highest levels that have been found in a community wastewater system, based on the scientific literature.

Our research has consistently found that while there are some pharmaceuticals detectable in crop tissue, the levels are extremely small–in the nanogram per gram (or parts per billion / ppb) range. This means that a person would need to eat a pound of urine-fertilized lettuce every day for 2,000 years to ingest a single dose of acetaminophen (Tylenol).

Other researchers have looked at the fate of pharmaceuticals in these situations, and have found results similar to ours: pharmaceuticals are sometimes taken up by crops, but in extremely small amounts, in the nanogram per gram (ng/g) range. Wastewater irrigation results in somewhat higher uptake levels because it usually involves repeated applications closer to harvest time. Still, at this point, our understanding is that the scientific literature indicates these quantities do not represent a significant risk to human health.

For people taking large amounts of medicine and using their own household urine in a garden, the levels in plants could be higher. We don't have figures for that, however, but you may want to exercise caution and dispose of that urine separately. 

Additionally, researchers at Rich Earth and elsewhere have tested charcoal filtration as an additional filtration treatment step for urine, and it removes most of the residual pharmaceuticals. Our current treatment train does not include this filtration, but if future study justifies the resources and energy required for this additional treatment, it could be implemented. We remain dedicated to better understanding the effects of pharmaceuticals on soil health, as well as how community perceptions of pharmaceuticals in urine fertilizer may vary.

There are a wide range of ways to divert and collect urine. We advocate for the ‘many tools in the toolbox’ approach - different people and contexts will prefer/require different options. Urine diversion can range from DIY containers (wide-mouthed laundry detergent bottles are common) to the informal urine collector Rich Earth designed (sold on Etsy or a sit-down version via Toilets for People) to a range of urine-diverting toilets (like the Wostman EcoFlush).

The informal portable collectors certainly aren’t for everyone, but it turns out that they work well for a lot of people! The urine diverting toilets are a more streamlined way to collect, but the permitting process and logistics for installation can be a hurdle. If you have a urine-diverting toilet (collecting all of your urine in a year) you may quickly find that you’re collecting a lot more urine than you can use in your home garden, so these are typically best where community scale collection and processing is available for farm-scale application.

Regarding health concerns, there are a few things to keep in mind.

• Pathogens: Urine from healthy people is actually generally pathogen free. For home gardeners, urine fertilizer does not need to be sanitized. Many people use urine in their home gardens without any treatment. The World Health Organization supports this practice if the urine comes from the same household that will be eating the produce, as long as you wait 30 days after fertilizing before you harvest produce that will be eaten raw. 
• Pharmaceuticals: We conducted six years of research in partnership with the University of Michigan to understand the fate of medicine compounds in urine fertilizer. Basically, when we flush our pee, drug compounds accumulate downstream with negative ecological effects that ramify up the food chain. When we reclaim our urine as fertilizer, those compounds are given a chance to be broken down in the soil and don't accumulate in crop tissue at a significant level. Read more about our research results here. However, if a member of the household is taking high doses of a medicine, for cancer treatment for example, one might want to dispose of that urine separately.

A heavy meat eater would have somewhat higher nitrogen content in their urine. It would not be easy to measure at home, but one could send a sample of the urine to a lab that does nutrient testing to determine nitrogen content. Our own testing has been a composite of community collected urine, and the NPK analysis is approximately .6-.1.-.2

We aren’t aware of any studies about the use of urine as a pest-deterrent, but anecdotally via our community science survey for home gardeners, we have heard that the use of urine as a fertilizer can have the secondary benefit of reducing some insect damage. Your idea about the salt content of the urine to specifically deter slugs is an intriguing one that we don’t believe has yet been studied. If you would like to do a home experiment about this, we’d love to hear how it goes via our survey! 

If you do try to use the urine as a foliar feed, we recommend diluting it with water to not burn the leaves. A ratio of 1:4 urine:water might be good to aim for.

This is Tatiana. That would depend on whether your plants needed a nitrogen boost  - i.e. on the developmental stage of the plant. If it's growing rapidly, then feeding a liquid nitrogen fertilizer like urine would work well. If you wanted a slower release source of nitrogen, then adding it to compost, or supplying at the same time of compost would be best. As a liquid, the nitrogen is taken up rapidly; if added to compost, some of the nutrients will be stored in the organic matter of the compost.