Soil regulates nutrients: Nature's recycling system

Closing the nutrient cycle again

Because nutrients are valuable resources, many strategies aim to keep them circulating rather than losing them from the system.

Composting is one example. Food scraps and garden waste are broken down into a nutrient-rich material that can be returned to the soil. This recycles nutrients and organic matter, improves soil properties, and supports new plant growth. Similarly, animal manure can also help close nutrient cycles. The nutrients it contains originally come from plants used as animal feed. When manure is applied to agricultural soils, these nutrients can be reused by crops rather than lost as waste.returns nutrients that originated from plants back to agricultural soils.

Even human waste contains valuable nutrients. Urine and feces contain elements such as nitrogen and phosphorus that originally came from food. Modern wastewater treatment systems mainly protect water quality, but new approaches increasingly explore how these nutrients can be recovered and reused. Examples include phosphorus recovery from wastewater and ecological sanitation systems designed to recycle nutrients more directly (Meinzinger et al., 2009; Harder et al., 2019).

Phosphorus is particularly important because, unlike nitrogen, it cannot be obtained from the atmosphere and depends on finite geological resources such as phosphate rock. Recovering and recycling phosphorus can therefore reduce pressure on these limited resources and keep this essential plant nutrient in circulation (Jupp et al., 2021).

Closing nutrient cycles does not mean copying natural systems exactly. It means designing human activities so that keep valuable nutrients circulating while reducing losses to the environment.

Soils play a central role in this process – not only by supporting plant growth, but also by helping ecosystems store, transform, and recycle the nutrients needed for life.

So, what happens to the nutrients that leave our bodies after we flush the toilet? The answer depends on the system they enter. They may become lost pollutants, or they may become valuable resources if we find ways to recover them and return them safely to soils.

If you understand German, take a look at the documentary “Kostbare Kacke – Zurück in den Kreislauf des Phosphors” which integrates diverse perspectives on phosphorus as a resource. The video is approximately 18 minutes long and was produced by BOKU University.