How do I spend my Saturday mornings you ask? Answer: scanning the peer reviewed literature for articles about using human urine as a nitrogen source in the garden, i.e. taking a leak in the watering can. As we’re currently hosting some excellent classes at our house taught by Darren Butler, a big proponent of what he calls “pee-pee-ponics,” I thought I’d take a look at the science of urine use.
Urine offers a free and readily available (at least after a night of beer drinking) alternative to organic nitrogen fertilizers such as blood meal. We’ve got a perpetual nitrogen deficiency in our vegetable beds and I hate buying industrial ag sourced items like blood meal. Urine is a great alternative.
To use urine in the garden you’ve got to dilute it with water, at least ten to one. Straight urine will burn your plants. Thankfully we don’t worry about our sauerkraut taking on a urine flavor:
Use of Human Urine Fertilizer in Cultivation of Cabbage (Brassica oleracea)––Impacts on Chemical, Microbial, and Flavor Quality by Surendra K. Pradhan, Anne-Marja Nerg, Annalena Sjöblom, Jarmo K. Holopainen and Helvi Heinonen-Tanski
Human urine was used as a fertilizer in cabbage cultivation and compared with industrial fertilizer and nonfertilizer treatments. Urine achieved equal fertilizer value to industrial fertilizer when both were used at a dose of 180 kg N/ha. Growth, biomass, and levels of chloride were slightly higher in urine-fertilized cabbage than with industrial-fertilized cabbage but clearly differed from nonfertilized. Insect damage was lower in urine-fertilized than in industrial-fertilized plots but more extensive than in nonfertilized plots. Microbiological quality of urine-fertilized cabbage and sauerkraut made from the cabbage was similar to that in the other fertilized cabbages. Furthermore, the level of glucosinolates and the taste of sauerkrauts were similar in cabbages from all three fertilization treatments. Our results show that human urine could be used as a fertilizer for cabbage and does not pose any significant hygienic threats or leave any distinctive flavor in food products.
As the study above noted, too much nitrogen (from any source) can cause pest outbreaks. And we do need to be judicious in our urine application in alkaline soils such as here in Los Angeles as urine has a high pH:
From Human urine – Chemical composition and fertilizer use efficiency by H. Kirchmann and S. Pettersson:
Stored human urine had pH values of 8.9 and was composed of eight main ionic species (> 0.1 meq L–1), the cations Na, K, NH4, Ca and the anions, Cl, SO4, PO4 and HCO3. Nitrogen was mainly (> 90%) present as ammoniacal N, with ammonium bicarbonate being the dominant compound. Urea and urate decomposed during storage. Heavy metal concentrations in urine samples were low compared with other organic fertilizers, but copper, mercury, nickel and zinc were 10–500 times higher in urine than in precipitation and surface waters. In a pot experiment with15N labelled human urine, higher gaseous losses and lower crop uptake (barley) of urine N than of labelled ammonium nitrate were found. Phosphorus present in urine was utilized at a higher rate than soluble phosphate, showing that urine P is at least as available to crops as soluble P fertilizers.
With some common sense urine application (i.e. not too much), it clearly makes a good fertilizer:
Stored Human Urine Supplemented with Wood Ash as Fertilizer in Tomato (Solanum lycopersicum) Cultivation and Its Impacts on Fruit Yield and Quality by Surendra K. Pradhan, Jarmo K. Holopainen and Helvi Heinonen-Tanski:
This study evaluates the use of human urine and wood ash as fertilizers for tomato cultivation in a greenhouse. Tomatoes were cultivated in pots and treated with 135 kg of N/ha applied as mineral fertilizer, urine + ash, urine only, and control (no fertilization). The urine fertilized plants produced equal amounts of tomato fruits as mineral fertilized plants and 4.2 times more fruits than nonfertilized plants. The levels of lycopene were similar in tomato fruits from all fertilization treatments, but the amount of soluble sugars was lower and Cl− was higher in urine + ash fertilized tomato fruits. The β-carotene content was greater and the NO3− content was lower in urine fertilized tomato fruits. No enteric indicator microorganisms were detected in any tomato fruits. The results suggest that urine with/without wood ash can be used as a substitute for mineral fertilizer to increase the yields of tomato without posing any microbial or chemical risks.
So go forth and pee (and dilute!). You can also, of course, just pee on the compost pile.
Many thanks to the always useful Google Scholar, one of my favorite gardening resources.