Urine has what plants crave

Urine has what plants crave

We need to talk about PP. For some reason it’s a taboo topic to talk about anything related to excretion. It’s understandable from a health standpoint to be a little bit concerned about poo. I get that. There are bacteria in poo that you wouldn’t like to have anywhere near you. But pee is an entirely different topic. Pee, or let’s be correct here, Urine, is very benign from a health standpoint. It has a near neutral pH when it’s fresh, it’s sterile and full of concentrated plant nutrients. Basically, it’s excellent fertilizer (not such a great beverage I have heard).

To really appreciate the value of Urine, I think a little excourse into the world of chemistry and history is in order.

The science


Nitrogen is one of the most abundant elements on the planet, with our atmosphere containing 78.09% elemental Nitrogen. It’s an essential building block of biological systems and therefore needed for agriculture.

What we know as the green revolution can largely be attributed to an increase in Nitrogen fertilizer use.

This fertilizer is nowadays made by the Haber Bosch process. This is a chemical process, that uses high pressures and temperatures and some catalysts to extract the elemental nitrogen in the air to create ammonium. The process uses around 2% of global commercial electricity production.

It’s also very useful to make explosives. The N in TNT being Nitrogen. This enabled the Nazis to carry on making explosives even after saltpeter embargos hindered access to useable nitrogen during WW2.

The use of Haber Bosch derived fertilizer is so strong nowadays that around 50% of the nitrogen in human tissue is derived through this process (don’t ask me how they calculated that). It also consumes a lot of natural gas (3-5% of world production) for providing the hydrogen for the process.


The first “mineral” fertilizer containing phosphorous was Guano. 30-50 metres high mountains of penguin poop. Guano was mined in some islands near Peru from around 1840, just to be depleted 30-40 years later, sending the peruvian economy into crisis at the time.

Guano island (wiki)

Guano was then supplanted by the invention and use of superphosphate, which is made from phosphate rock. Phosphate rock is mined in big open cut mines around the world. Despite the obvious fossil nature of rock-mining for fertilizer there are two major discomforting properties of the rock-phosphate topic. Firstly, the easy to get, high quality rock phosphate reserves have been mined for so long, that the remaining reserves have an increasing amount of heavy metal contamination (mostly Cadmium). Cadmium is not very healthy when ingested in large quantities.

It’s a contested topic, because the deposits high in Cadmium are mostly located in Northern Africa. Which brings us to the second issue. The remaining large deposits of phosphate rock are absurdly concentrated in just one country, with it’s fair share of dodgy annexation moves (West Sahara), namely Morocco.

Global distribution of phosphate rock reserves (wiki)

This monopoly and the need to remove the Cadmium from the phosphate rock could lead to increased prices for phosphate fertilizer, which is a very important part of agricultural systems. Use of phosphate rock was even advocated by Bill Mollison, co-creator of Permaculture, because it’s simply essential for life (you might recall that DNA contains phosphorous as it’s backbone).

The dependence on this material and the risk to global food security, should prices increase, is of increasing concern worldwide.

Comparable to peak oil, some people summarise the developments around this element as Peak Phosphorus.


Because it contains a lot of Nitrogen, urine was used as industrial feed stock for many of the things that ammonia is used today, like gunpowder and fertilizer. Aged Urine was known as Lant, wikipedia claims it was used to flavour ales (which explains a lot about the taste of some british beers). Urine also contains a not insignificant amount of phosphorous. Because it is a source of these valuable plant nutrients, urine is used as fertilizer in some scandinavian countries. “urine P [phosphorus] is at least as available to crops as soluble P fertilizers.

Agricultural Use and Sustainability

Using urine in agriculture also helps combat another problem, which everyone in the environmental field knows about. Eutrophication. Also known as algal blooms. In easy words, Nutrients that are good for plants, like N and P, are also good for algae, and if you add too much of those to waterbodies (like rivers), then the algae grow a lot. After they have grown they decompose at the bottom of the river or lake, which uses up all the oxygen and lots of fish die. Many dead fish are not good PR and governments generally avoid these things from occuring.

In places where there is no wastewater treatment, using urine in agriculture makes more sense, because the valuable nutrients can be taken up by plants and are not feeding algae that then kill all our friends with gills.

Still, urine is a “mineral” fertiliser, which can be overdosed (leading to eutrophication through groundwater inflows into water bodies). It also contributes to declining organic matter content in soils, because decay of organic matter (carbon compounds) get turbocharged with ammonia and nitrate addition, just like the Haber Bosch nitrogen and the rock phosphate fertilizer does.

Recovery Efforts

I visited some places that try and develop systems to recover urine for fertilizer use. One of the most well-known worldwide is eawag in Zürich. The swiss aquatic research institute has been working on urine diverting toilets for decades and is now coming up with yet another sophisticated way to determine whether what’s going into the bowl is the real deal or just plain ol’ water.

Conductivity meter powered urine diverting toilet bowl.

The bowl pictured above uses a conductivity meter to determine the amount of dissolved ions in the liquid. Urine has more and the valve opens up to let the juices flow to the recovery facility in the basement.

Another research institute in Vienna, alchemia nova, is working on plant based public toilets, to prevent eutrophication in rivers through too many nutrients, but with a beautiful, green urine-loving jungle. The urine is filtered through a cascade of plants, which take up the nutrients and who house bacteria that convert it back into nitrogen gas.

Spiritual dimensions

But there are other, non-technical, dimensions to Urine (which you have probably never explored). Re-using your own excretions (not just eating your buggers, mate) for productive plant growth, reconnects you with the global cycles we are all still part of. The dung of cows fertilizes the grassland that they depend on. Similarly, our civilisation depends on a few inches of top soil, which is basically on life support since we started plowing and fertilizing it like never before.

City dwellers are far removed, through multiple levels of abstraction, from the origins of their food supply. But through keeping and reusing some of your urine or even thinking about composting toilets, when travelling (or at home), can put us back in touch with the place from where we all came from and where we will go back to. Earth.

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