An odd question about shit

Does the average human produce enough faecal waste to fertilise the land necessary to feed that human?

I rather assume not as it would likely violate the conservation of something or other.

But does anyone actually know?

The reason I ask: if yes then an entirely vegetarian and organic agriculture is possible. We need no new abstraction of fertiliser from the environment nor do we need animal wastes.

However, if not, then we need either animal waste or we need \”artificial\” fertilisers. Which means dumping either the vegetarian option or the organic.

So it would be interesting to know: can humans shit enough to fertilise the crops that feed humans?

29 thoughts on “An odd question about shit”

  1. The type of system Tim’s describing probably wouldn’t be reliant solely on human fertiliser, but would likely include at least an element of green manure, as well.

  2. It’s not just a question of quantity but quality too – it’s illegal to use human waste for fertiliser in NZ, and probably in other developed countries, because of the risk of infection from E. Coli and other nasties which pass through the human digestive tract.

  3. What you’re asking here is whether you can have a closed loop on the minerals etc needed to sustain the system. If it was just a matter of the sh1t (& the pee,of course), yes, if the humans ate 100% of the agricultural produce with none wasted. Probably require living on a diet of algae.
    Trouble is, no systems 100% efficient. You loose stuff out the cycle. Even on a planet wide basis, all the nutrients would eventually end up in the sea. If it wasn’t for plate tectonics, mountain building & erosion, the planet’d probably be sterile by now.

  4. And ‘green manure’ as above is pure woo in this context. You can’t add nutrients, other than nitrogen by using a nitrogen fixing crop. To add nutrients, you’d have to grow the ‘green manure’ on other land where it would take up the nutrients. Then process it. Another name for that would be grazing & livestock, wouldn’t it? And much more energy efficient.

  5. Sorry Tim. There is no practical method of running such a closed system, thus the question lacks importance.

    There are problems with the inputs (eg nitrogen fixating plants and animals that shit in the fields) and with the outputs (soluble salts from urine etc that go to the sea and help the fishes). We eat some wild animals/birds/fish and the amount is variable between regions and cultures.

    Also, being vegetarian does not provide a balanced and healthy diet: supplements are needed. Most of us are not vegetarian but omnivorous. Thus domesticated animals need to be included within the system.

    However, you might find the following table useful, from Wikipedia: http://en.wikipedia.org/wiki/Fertiliser#Application

    It shows, for the total population of 2,372million of those 11 countries (about % of the world population) that total nitrogen fertiliser use is 41.3Mtonnes per annum, with 27.4Mt being on non-animal-feed use. This equates to total use of 17.4kg/person and non-animal-feed use of 11.55kg/year.

    Also, for you on the production side, we have Guidelines on the Use of Urine and Faeces in Crop Production. Note particularly that urine content is vastly more ‘important’ than faeces content, for nitrogen; this is down to the solubility issue. Page 5 is particularly useful. It gives, per person/year of nitrogen: 4,000g in urine and 550g in faeces.

    Thus human excrement would (at 100% extraction) provide 26% of current total nitrogen fertiliser use and 39% of current non-animal-feed use.

    My invoice will follow shortly.

    Best regards

  6. Incidentally, there’s periodic attempts at doing this stuff with various ‘ark’ projects. The glorious fuck-ups are educational. We’ve 10,000 years of of agricultural experience behind us & we do seem to have come to the conclusion, mixed farming is about the closest you can get to replicating the natural cycle.

  7. I think the most important questions are:

    1) What line of thought/conversation led to this?
    2) What were you drinking/smoking at the time?
    3) Where can I get some?

  8. Didn’t the Japanese do this for thousands of years?

    Since the main element of Japanese diet was rice and a few slivers of fish, I’d say no.

    Unless they were fertilising the fish…

  9. You’re forgetting about Ritchie, Guardian journalists et al. They pump out enough shit to fertilise the planet comfortably.

  10. Our local sewage treatment plant for a city of about 1M population is making a few bucks selling the treated sewage solid waste leftovers to local farmers. The clean water goes into the river, downstream of the inlet, the muck goes to the fields.

    There are rules and regulations about what kind of crops it can be used for. Lettuce is a no-no, I hope.

  11. However, if not, then we need either animal waste or we need “artificial” fertilisers.

    Animal’s don’t produce nutrients, they excrete whatever they’ve ate that isn’t added to their bones/meat. Using green-manures with nitrogen-fixing legumes (on a slightly smaller area than feed) has the same effect.
    I think I remember though a german paper that concluded that the most efficient organic system (food per area) is using ruminants to produce milk/and a small amount of meat(eating partly nitrogen-producing legumes), and fertilize food-crops with their waste.

    As mentioned before, there is an issue with contaminants and human sewage. Bacteria can be dealt with heat-treatment, fermenting in a biogas-chamber and/or composting. The problem with using your average sewage is the building up of metals in the soil with frequent re-application. Using urine is ok, but there isn’t going to be any large-scale separation of it. If/when phosphorous gets scarce, there’s a good case for extracting it from sewage.

    Tim adds: Phosphorous. Interesting that. I know a company recycling that right now. It causes a build up of scale inside pipes (called “sterrite”) and the reduction in maintenance costs pays for the equipment to extract it. The phosphorous is therefore free but can be sold to the fertiliser peeps. Not hugely valuable, a few hundred $ per tonne, but nice all the same.

  12. Yeah that’s the method that so far rives the best quality fert.. Sewage plants will often need to remove P anyway, but most use iron to precipitate P, which makes it useless as fert.. I know a canadian corporation chat delivers a sterrite precipitation system, Ostara I think. Is that the one?

    Tim adds: Think so…

  13. Amish anyone? Pretty sure they don’t import fertiliser. One of the more successful organic farmers.
    Saw something that said at best they get half the output of a modern farm, pretty good considering the lack of industrial pesticides and fertiliser.

  14. Not really relevant to UK, but in western US states, salmon go to sea, get fat, come home, get eaten by bears (and we know where they shit), lay eggs, get eaten by rainbow trout (who also eat a lot of eggs), who in turn get eaten by bears, bearded men from Oregon etc. So nutrients flowing to sea (BIS 4) is not an insurmountable problem.

    I am of course impressed by the surprising knowledge of shit exhibited by this blog’s followers.

  15. So Much For Subtlety

    john miller

    Didn’t the Japanese do this for thousands of years?

    Yes they did. Japan does not have forgiving soil like China. Nor does it has useful rivers like China and Egypt. So if you read Tokugawa history books that deal with peasants, it is a long and constant struggle to maintain the fertility of the soil. Yes, they replaced as much sh!t as they could – which presumably led to serious stomach problems of various sorts as parasites would not have a “break” in the gut of some other animal. They even collected “night soil” from the cities and put it on fields if they could.

    But they also had to constantly search out extra fertilizer. Which meant peasants stripped the mountain sides as bare as they dared for green leaf material. And fisherman caught fish just for fertilizer.

    The lack of meat in the diet is probably due to the success of this effort – population grows until it hits a natural limit. So space for animals shrinks – except for ducks, chickens and pigs.

  16. I suspect that it would provided it were integrated with healthy doses fromt eh grauniad comment is free columns

  17. Reserves of nitrogen amount to about 100 million years of current usage, so even if we fired shit into outer space it would take quite a long time to deplete the reserves.

    Morocco alone has about 2,000 years of readily minable phosphorous at current rates of use.

    So I wouldn’t worry about Peak Shit, Tim.

  18. I remember reading, back some 50-60 years or so, about something called “the crab cycle” (I suppose it could be googled if one were so inclined).

    A tribe of natives lives in marshes somewhere on the Brazilian coast. They live in homes built well above the water level, supported on “stilts.” The natives live primarily on crabs caught in the marshes below their homes. When it’s time to “go to the bathroom,” they do so very conveniently–through a hole in the floor of their abode. Of course, the excreted material becomes nutritive material for the flora and fauna of the marsh (including the crabs that provide the mainstay of the local diet.

    Studies of bothe the human and crab populations over some period of years shows both getting progressively smaller–probably due to a significant amount of the total nutrients being washed further away (out to sea, perhaps).

  19. Fred Z:

    The city of Milwaukee, Wisconson, has been marketing their sewage-system recoverables for very many years-at least the better part of a century. It’s sold in many different retail venues
    as “Milorganite.”

  20. I am of course impressed by the surprising knowledge of shit exhibited by this blog’s followers.

    With Arnald here and Ritchie chez himself, nevermind the manifold excreta of CiF, we’ve developed quite an understanding of the smelly side of human output.

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