Urine as Fertilizer

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Last year I compiled an essay about urine as fertilizer. I’m going to copy and paste most of it here for anyone interested in this topic:

Fertilizer Value

The N-P-K ratio of human urine is approximately 11-2-4, depending on diet and individual biological factors (Penn). Compared to another popular liquid fertilizer, fish emulsion—in which a typical N-P-K ratio is 2-4-1 (Enroth) — urine has a quite high ratio of nitrogen in proportion to its phosphorus and potassium content. According to analysis conducted by the Rich Earth Institute, human urine can be expected to contain 0.05lb nitrogen, 0.008lb phosphorus, and 0.017lb potassium per gallon (“Using Urine as a Fertilizer in Home Gardens”).

Before delving more deeply into the properties of urine as a fertilizer, let us make a comparison of scale: Industrial nitrogen fertilizer is typically applied to corn fields at rates near 100lb to 200lb per acre per year. In order to fertilize a monoculture corn field accordingly and produce 150 bushels of corn per acre, 2,000 to 4,000 gallons of urine would furnish the appropriate amount of nitrogen per acre. The same amount of urine contains approximately the correct amount of potassium for the same crop, whereas approximately 7,000 gallons of urine would be required to furnish sufficient phosphorus to the one-acre corn field (Silva).

Urine in its liquid form occupies a greater volume than its equivalent in dry mineral fertilizer, however it can also be said that human urine is abundant. Normal production of urine ranges from 0.21 gallons to 0.53 gallons per person per day (“Urine 24 Hour Volume”). Based upon that figure, New York City, with a population of 8.258 million, produces at least 1.7 million gallons of human urine per day (U.S. Census Bureau).

Because urine is produced most abundantly in areas of high population density, such as metropolitan areas, it can be surmised that large-scale implementation of human urine as an agricultural fertilizer would require transportation of the resource from urban areas to nearby rural areas. It can further be concluded at the time of writing this article that urine fertilizer is generally more practical for application on small farms than large ones.

Regulations

There are no established regulatory pathways for the recycling of urine as fertilizer. According to the Rich Earth Institute: “The Food Safety Modernization Act, and other federal, state, or local regulations may restrict the sale of some crops fertilized with urine” (“Using Urine as a Fertilizer in Home Gardens”). The organization’s work to establish distinct regulations for urine recycling is described thusly on richearthinstitute.org:
“Rich Earth worked with the Vermont Agency of Natural Resources Watershed Management Division to create unique regulatory pathways for permitting the collection, transport, treatment, and land application of urine as a fertilizer in Vermont. We are now working to support the creation of regulatory pathways in other states, using our permits as a model.”

Dilution

Considering urine’s proportionately high nitrogen content, its application as fertilizer should be tailored to the soil and crop to which it is applied. Dilution of urine in water is common. A survey conducted by the Rich Earth Institute found that respondents, mostly home gardeners, most commonly diluted their urine in water to ratios from 1:3 to 1:5. Splashing of undiluted urine on crop foliage should be avoided, as nitrogen can burn plant foliage. That being said, when urine is applied directly to moist soil, dilution is unnecessary (“Using Urine as a Fertilizer in Home Gardens”).

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Studies have been conducted to demonstrate urine’s effectiveness as a fertilizer. A team of researchers from Niger, Germany, and the U.K. conducted an experiment with women farmers in Niger who were struggling to produce crops for sale due to the high cost of commercial fertilizers and scarcity of animal manure. The researchers compared a control group of farmers using their traditional methods to grow wheat, and a second group fertilizing their wheat with urine provided by the farmers themselves. The urine amendment was fortified with a small amount of animal manure. Fields fertilized using the urine amendment produced 30% more grain. Two years subsequent to the experiment, the researchers found that over a thousand women in the area had adopted the use of urine as fertilizer (Yirka).

Surendra K. Pradhan and other researchers at the University of Kuopio, Finland conducted experiments comparing the use of urine fertilizer and industrial mineral fertilizer in production of pumpkin and cabbage. The researchers determined that pumpkin plants fertilized with urine produced a greater yield of pumpkins than unfertilized plants, but a lesser yield of pumpkins compared to the plants given mineral fertilizer. Pumpkin plants fertilized with urine produced more vine growth than both other groups, but urine-fertilized plant tissues demonstrated lower levels of potassium than the mineral-fertilized group, which may explain why fruit production was not enhanced in the urine-fertilized plants to as great a degree as in the mineral-fertilized plants. Plants fertilized with urine also contained higher levels of chloride ("Fertilizer Value of Urine in Pumpkin”).

In a similar experiment comparing urine fertilizer and mineral fertilizer in production of cabbage, urine was found to be a highly suitable fertilizer for cabbage. In metrics of growth and biomass, as well as insect damage, cabbage plants fertilized with urine performed slightly better than cabbage plants fertilized with industrial mineral fertilizer. It was once again noted that levels of chloride were higher in plants fertilized with urine than the mineral-fertilized and control groups. Sauerkraut produced from the urine-fertilized cabbage was similar in flavor and microbial qualities to the sauerkraut produced from the other two groups (“Use of Human Urine Fertilizer in Cultivation of Cabbage”).

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Sodium and Chemical Contaminants

Human urine is high in sodium and chloride, which are essential nutrients for humans but can be harmful to plants when they build up to high concentrations in the soil. Soil salinity and sodicity have been shown to increase upon heavy fertilization with urine, and can mount to levels which result in decreased crop growth. A decrease in soil pH subsequent to fertilization with urine has also been demonstrated, but proved temporal. Due to its salt content, urine fertilizer is most suitable for salt-tolerant crops and/or use in humid climates with sufficient precipitation to leach salt out of the soil (Yongha). Soil already suffering from sodicity due to excessive urine fertilization can be remediated: researchers have demonstrated, in water-scarce contexts where rain is not normally sufficient to wash away salt, freeing of sodium salts from the soil can be enhanced by the addition of calcium (Mokhtar).

The Rich Earth Institute has conducted research on the persistence of pharmaceuticals in urine, soil, and plant tissues and discovered that persistence and uptake of pharmaceuticals in crops fertilized with urine is extremely small; furthermore, soil organisms are relatively effective at breaking down pharmaceuticals, whereas pharmaceuticals in wastewater are persistent and have negative effects on downstream aquatic life (“Pharmaceuticals”). When interrogating potential contamination issues from the use of urine fertilizer, it is relevant to note that potential toxins found in urine cause considerably more harm when added to water systems than when added to soil.

Bacteria

Urine poses little risk of spreading pathogenic bacteria. Fresh urine contains low numbers of microorganisms. Furthermore, when stored for several months, human urine attains a pH of 9 which is sufficient to prevent the growth of pathogens (Rumeau). The World Health Organization recommends that urine be applied to the ground as fertilizer without any additional treatment if it originates from the same household that will be eating the produce. Sanitation is recommended if the urine is supplied by different households than those who will consume the produce. According to the WHO sanitation can be achieved by storing urine in an airtight container at a temperature of at least 20°C or 68°F for six months. Alternatively, urine can be pasteurized before use as fertilizer (“Using Urine as a Fertilizer in Home Gardens”).

Fermentation

During storage of urine, urea is converted into ammonia which can be lost to volatilization upon exposure to air. This results in loss of nitrogen value, as well as increased odor emissions and air pollution. These issues can be addressed through lactic acid fermentation of urine, which decreases nitrogen volatilization. Researchers lacto-fermented urine in a closed container for 36 days, using inoculum from sauerkraut juice. The resulting fermented urine demonstrated increased effectiveness as a fertilizer compared to stored urine, and was also rated by test participants as significantly less odorous than stored urine. While the comparatively high ammonium concentration in stored, unfermented urine offers sanitation benefits due to increased pH, there are significant drawbacks associated with the volatilization of ammonia. In order to reduce the production of ammonia, lacto-fermentation should be initiated with fresh urine prior to storage. The result approaches a pH of 4 (Andreev). This research suggests lacto-fermented urine may be preferable to unfermented stored urine, although both can be utilized as fertilizer.

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References

  • Andreev, N., et al. “Lactic acid fermentation of human urine to improve its fertilizing value and reduce odour emissions.” Journal of Environmental Management, vol. 198, 2017.
  • Enroth, Christopher. “Scale up your garden’s health with fish emulsion fertilizer.” Illinois Extension, University of Illinois Board of Trustees, 25 Apr. 2022, extension.illinois.edu/news-releases/scale-your-gardens-health-fish-emulsion-fertilizer.
  • Mokhtar, G., et al. “Soil Fertilization with Human Urine and Salinization Risks.” IWARESA 2018
  • Book of Abstracts, IWA Regional Conference of Water Reuse and Salinity Management, Murcia, 2018.
  • Penn, Scarlett. “Taking the pee: is urine a good fertiliser?” Low-Impact Info, News, and Debate, lowimpact, 2023, Taking the pee or a golden opportunity: is urine a good fertiliser?.
  • Perry, H. M., and Elizabeth F. Perry. “Normal Concentrations of Some Trace Metals in Human Urine: Changes Produced by Ethylenediaminetetraacetate.” The Journal of Clinical Investigation, vol. 38, no. 8, 1959, p. 1458.
  • “Pharmaceuticals.” Research Results, The Rich Earth Institute, 2024, Rich Earth Institute : Pharmaceuticals.
  • Pradhan, Surendra K., et al. “Fertilizer Value of Urine in Pumpkin (Cucurbita maxima L.) Cultivation.” Agricultural and Food Science, vol. 18, 2009.
  • Pradhan, Surendra K., et al. “Use of Human Urine Fertilizer in Cultivation of Cabbage (Brassica oleracea)––Impacts on Chemical, Microbial, and Flavor Quality.” Journal of Agricultural and Food Chemistry, vol. 55, 2007.
  • Silva, George. “Nutrient removal rates by grain crops.” MSU Extension, Michigan State University, 10 Oct. 2017, www.canr.msu.edu/news/nutrient_removal_rates_by_grain_crops.
  • “U.S. Census Bureau Quick Facts: New York City, New York.” United States Census Bueau, 1 July 2023, www.census.gov/quickfacts/fact/table/newyorkcitynewyork/PST045222.
  • “Using Urine as a Fertilizer in Home Gardens: Frequently Asked Questions.” Rich Earth Institute, The Rich Earth Institute, 2019, richearthinstitute.org/wp-content/uploads/2019/12/Home-Use_Manual_05.pdf.
  • “Urine 24 Hour Volume.” MedLine Plus Medical Encyclopedia, National Library of Medicine (US), 20 Aug. 2023, Urine 24-hour volume: MedlinePlus Medical Encyclopedia.
  • Yirka, Bob. “Testing the Use of Human Urine as a Natural Fertilizer for Crops.” Agriculture News, Phys.org, 21 June 2022.
  • Yongha, Michael Boh, and Joachim Sauerborn. “Effect of NaCl-Induced Salinity and Human Urine Fertilization on Substrate Chemical Properties.” Open Journal of Science, vol. 4, no. 1, January 2014.
  • Zhou, Yige, et al. “Efficient recovery of phosphate from urine using magnesite modified corn straw biochar and its potential application as fertilizer.” Journal of Environmental Chemical Engineering, 2024.
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Thank you for sharing this information. I live in a dry climate and probably need to be careful of using too much in one area. But it made me wonder if I could use it to inhibit weed growth in an area where I’m not trying to grow crops by allowing some sodium buildup. As a bonus, would it keep dogs away, especially those that like to leave behind a personal gift, or would it encourage them?

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That’s a good question, I can’t find any reliable info on that.
I’m imagining it would only repel a dog if the dog is scared of you.

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Perhaps a little experimentation is in order!

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We use our urine as fertiliser every other day and dilute 1:1 as we live in a wet area. The hedge growth accelerated a lot when we started doing that.

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We have used it around the perimeter to deter foxes. Not sure how effective that was, but the fox stopped coming (after killing two hens).

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When I want to get rid of a vigorous Siberian elm root that will not stop sending up eight bajillion suckers every two weeks, I dig deep until I find that root, leave the hole open, and pour lots of undiluted urine on it every day for about two months. That seems to be enough to kill that root. It’s the only thing I’ve found that works (other than Roundup, which is dangerous long-term). So yes, killing weeds with undiluted urine can totally work.

It might also be a good idea to try something like that on a patch of grass you want to kill – overfertilize it with tons of urine for a week or two first, and then add cardboard on top with a whole bunch of mulch over that. Maybe that combination would kill the grass faster? (If nothing else, you’ll get a nice “compost in place” effect to make the soil lovely when you are ready to plant into it later.)

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Some interesting gems in this document sent to me from @DebbieA

like this "More puzzling was the resistance of plants to pests and diseases. In one instance, a set of tomato plants was growing near a tree heavily infested with the white fly. Many of these insects would fly around the plants ordinarily so prone to being attacked by them but not one landed on the leaves. They simply flew back to the tree. Eventually, an article in a German scientific journal gave us the clue. The composting process taking place inside the container produced substances that helped the plants become not only stronger, but also resistant to pests. An added bonus. " (My question here… are they sure of that and how??)

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