Environmentalists advise us against chemical fertilizers and tell us to use organic alternatives instead. Sri Lanka tried to do that, and now its economy is in a total shambles (not only because of that, but partly because of that): they had crop failures and were forced to buy food from abroad, depleting foreign reserves. It also hurt the country's tea and rubber exports. Is it really such a good idea after all?

  • The situation in Sri Lanka may be more complicated than reported in the media. I wonder whether the right type of organic fertilizer was used. Did it have all the requirements needed by the crops and did the farmers have enough fertilizer?
    – Fred
    Jun 18, 2022 at 12:01
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    Based on this q on Skeptics.SE, it's my understanding that the problems in Sri Lanka stem from the attempt to make the transition with no training for farmers and no understanding of the proper way to transition farming methods.
    – LShaver
    Jun 18, 2022 at 12:15
  • it's possibly more helpful to think about it as "industrial farming" or "chemical farming"... there's a whole interlinked web of systems that go into the "green revolution" modern farming systems. Similarly with organic and especially sustainable farming techniques. Although worth noting that agriculture is traditionally extractive and short term, we have few example of agricultural societies lasting more than a millenia and the major one was deliberately exterminated (the British invasion of Australia). Some useful terms to look for are "regenerative farming" and "permaculture".
    – Móż
    Nov 15, 2022 at 22:20
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    You will find the objectively measured nutrients ( N, P, K ) , in organic fertilizer is inadequate for substantial crop production. Nov 16, 2022 at 0:44

2 Answers 2


Recycling. Processing sewage is most effective means recovering rebuilding fertilizer use. Human reuse of excreta is thousands of Yeats old.

China, Japan, Korea did so, China in particular did so foe four millennia. Collapse of Rome eliminated sewers as method of waste disposal for centuries, unlike Medieval Europe where waterborne diseases proliferated due to collapse post Roman hygiene. China's waters were drinkable up until 19th-20th century. Documented in RF Kings book,"Farmers for Forty Centuries "


Organic fertilizers are in my opinion a very good idea but require some development to make them economically feasible. The idea is that whatever nutrients are in crops don't disappear but will be in animal/human excrement. It's a 100% efficient process since you can't make matter appear or disappear out of thin air (leaving aside nuclear processes that don't really happen here). So food security won't be compromised, we will have enough of these organic fertilizers for 100% circular economy. We just need to learn to use the correct amount.

If every farm has land for growing crops and a number of animals for meat and milk, most of the crops goes to animals and a very little amount to humans, as animal agriculture is very inefficient. It makes sense to use that animal excrement as fertilizer. Only very little of the nutrients is lost (the amount that humans eat), so some nutrient replacement is necessary using chemical fertilizers.

In today's world, however, there are farms that specialize in growing crops and farms that specialize in meat and milk. It's more economical that way. For example, automated milking machines make sense only if there are a lot of cows, so we will have concentrations of cows producing heavy excrement with some nutrients, and long distance away are the plant-producing farms that have no animals. Unfortunately, transporting that excrement to farms that grow crops may not make sense, since the journey would be long, the product is so heavy and fuels are expensive (and for long journeys battery electric vehicles don't make sense). A solution could be to somehow make two waste streams from that excrement, one that is poor in nutrients but could be used for biogas for example, and another that is rich in nutrients. I think we don't have economically viable commercial solutions for making that nutrient-rich stream yet.

Another problem is that due to limited ability to grow crops on finite land and increasing population and wealth in developing countries, it is imperative that most of the population of this planet goes vegan (not necessarily fully vegan but 70% vegan at least). Without that, we can never produce enough food to feed all starving people. Animal agriculture is just way too inefficient. In this case, the nutrients in human excrement are in the wastewater. So wastewater treatment plants should in the future extract those nutrients and make recycled fertilizer out of them. Otherwise we will lose all of the nutrients.

Nitrogen is something that can be included in fertilizers using chemical processes, no sustainability problems there. Air is mostly nitrogen, and nitrogen can be extracted from it by making liquid air and distilling it. To fix that nitrogen, we need hydrogen, but fortunately that can be made from water and renewable electricity using electrolysis. The main problem in chemical fertilizers is that we have limited phosphorus reserves, so a circular economy would really help there. Fortunately, what phosphorus reserves we have go a long way, so developing solutions to make organic fertilizers make economical sense will have enough time.

I suspect, though, that the final solution will not be to distribute human or animal excrement on crop-producing fields directly but rather make a dense nutrient-rich "semi-organic semi-chemical" fertilizer from recycled nutrients, stopping most phosphorus mining.

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    But with the current technology, we can't do without chemical fertilizers, can we? They say we don't have enough manure to keep crop production at its current levels. We would have to keep more cattle and grow more grains to feed them (doesn't sound sustainable) Jun 20, 2022 at 22:17
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    Your answer would be improved by a whole truckload of citations
    – RedSonja
    Jun 21, 2022 at 9:24
  • Nitrogen is not a problem as substance, but it is very much an energy problem in terms of sustainablilty. I crunched numbers some years ago, and came to the conclusion that about 1/6 of the worldwide fossil gas consumption goes into the production of nitrogen fertilizer. Nitrogen losses to the air or ground water are a concern for organic fertilizers as well, a quick googling told me an order of magnitude of about 10 % (for fermented manure), but with a range that can be as low as 2 %, but also as high as 40 %. (It still may be most effective to let parts of the nitrogen of the manure ... Jul 29, 2022 at 7:54
  • ... be converted to N2 which escapes into air during fermentation and instead have biological nitrogen fixation by e.g. mixed crops with Fabaceae (legumes/peas/beans).) However, right now, IMHO the energy aspect is not to be neglected. Jul 29, 2022 at 7:58
  • Yes, today natural gas is massively used to make hydrogen, to make ammonia, to make fertilizers. However, we need to look into the future. There's massive land wind power resources in many countries (like Finland), and even more massive offshore wind resources practically everywhere. Wind power is already competitive. Green hydrogen projects are popping up all the time. It won't take long until green electricity produced ammonia is used to make fertilizers.
    – juhist
    Nov 19, 2022 at 10:21

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