Growing plants on the balcony? I do, and tomatoes need lots of fertile soil. Worms make fertile soil for free. In my bicycle shed (typically Dutch I suppose). While in Iowa last year, I was inspired by the ‘urban ag movement’ and I saw an instruction on the cityfarmer website which led me, on return, to close my household nutrient cycle better by composting my own vegetable food scrapes. It took a while to get the right balance in the three-story box that we build out of plastic storage boxes but it is working well now. The worm castings are extremely fertile as is the liquid (their pee and the muck water from the food scrapes). And it is fun, I think, to compost and close part of the cycle in this way.
Back in the 19th century, Marx was worried about disrupted nutrient cycles since large amounts of nutrients were traveling to city and town while none of that returned to the field. During 1830 – 1870 the depletion of the soil fertility was the overriding environmental concern in Europe and the US. Prior to the discovery of chemical fertilizers, bone and Peruvian guano (accumulated dung of sea birds) were massively imported in Britain to relieve soil exhaustion while other countries had to search for alternatives because of the British monopoly on guano (Foster 1999).
“The second agricultural revolution, associated with the application of scientific chemistry to agriculture, was therefore at the same time a period of intense contradictions” Foster (1999:377) writes. The discoveries in soil sciences also made farmers even more acutely aware of the depletion of the soil and the need for fertilizers. Marx understood that soil fertility is “not so natural a quality as might be thought; it is closely bound up with the social relations of the time” (Marx in Foster 1999; 375) captured in his concept of metabolism. His writings about metabolism can be seen as one of the earliest writings on what is now called ‘sustainability’.