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”).