By JOSEPH R. HECKMAN, Ph.D.
Fertilizers are expensive and the current supply is limited. Farmers interested in sustainability are naturally interested in alternative nutrient sources and ways to use fertilizers efficiently.
I want to share with readers of The Natural Farmer my experience using a valuable natural resource; it is something all of us produce every day. The substance I am writing about is urine.
In 2021, I collected my urine and saved it in containers to experiment with its potential use as a fertilizer. After the first cutting of hay, I took some of the accumulated urine and spread it on a field section to spell out the letters: NPK. The photo taken about three weeks later shows a nice green-up and growth response to the applied urine.
The average adult produces about 100 to 150 gallons of urine per year. The design of modern sanitary systems normally causes urine to be wasted as it is flushed away to sewage treatment plants.
Nutrients contained in 100 gallons of human urine would typically be supplied in pounds: 4.8 Nitrogen, 0.3 Phosphorus, 1.3 Potassium, 0.4 Sulfur, 1.2 Sodium, 0.02 Calcium, 0.01 Magnesium, and 0.002 Boron. This is an average nutrient excretion as urine from one person over a year. Values, however, will vary depending on diet.
A typical fertilizer recommendation to produce grass pasture or hay for livestock feed is to broadcast 25 to 50 pounds of N after each pasture rotation or harvest. Thus, about 500 to 1000 gallons of urine applied per acre as a liquid fertilizer would be needed to satisfy that N recommendation. That application of urine will supply at the same time useful amounts of other nutrients.
Much of the N contained in urine is potentially volatile as ammonia which can go off into the atmosphere. Thus, to minimize ammonia volatilization and conserve the N for crop uptake, the urine should be applied just before a rain shower is expected or irrigation can be used to move the N into the soil.
Note that a 1000-gallon per acre rate is the amount of urine that can be produced by ten people per year. Now consider a farm that directly markets meat or milk from an on-farm store. Can one imagine a system where customers are invited to bring their urine collection back to the farm to close the nutrient cycle?
Perhaps it could be called “Community Supported Soil Fertility”. This would be a new twist on Community Supported Agriculture or CSA wherein this case the objective is feeding the soil that feeds us.
Certified organic farms might be reluctant to use urine as a fertilizer. (So far as I am aware, urine is not on a prohibited list but as always check with your certifier before land application of any material). Nevertheless, there might be other readers of The Natural Farmer with sustainable farms that function much like organic farms but without organic certification.
I am not suggesting urine be used for the production of food crops directly consumed by people, but rather the focus should be on grasses that have a high demand for N and are grown for livestock feed.
To learn more about using urine as a fertilizer, check out the works of the Rich Earth Institute: http://richearthinstitute.org/
This organization has considerable experience collecting and turning human urine into fertilizer. Located in southern Vermont, the Institute conducts field trials with human urine collected from the local community. The Rich Earth Institute reports that grass hay yields from urine application are equivalent to that produced from commercial fertilizer.
JOSEPH R. HECKMAN, Ph.D. is an Extension Specialist in Soil Fertility.
heckman@njaes.rutgers.edu