Our review of estimates of P recycling in the human P cycle show considerable variability and uncertainty, but today it appears that only about one-quarter of the fertilizer P used in agriculture is recycled back to fields. The rest is lost to the cycle, and much of this loss ends up in waterways, causing expensive eutrophication problems. As with other nonrenewable natural resources, a sustainable P supply is not assured, and some projections show economically viable mineral reserves being depleted within decades. In addition to our review of human effects on the global P cycle, we present a number of sustainable solutions that involve closing the loop on the human P cycle. Some of these solutions are relatively straightforward but many involve overcoming considerable infrastructural or institutional inertia [Childers 2011: 123].
Economically viable mineral phosphorus reserves may become depleted within decades, threatening global crop production for a growing world population. The authors discuss this problem in relation to human P cycle, where the vast majority of mined phosphorus is not recycled back onto farm fields, but is released more or less irretrievably into the environment, polluting water bodies. “There are considerable social and environmental costs of P being lost from the currently ‘open’ human P cycle” [Childers 2011: 120].
The authors present several options for closing the human P cycle at the points of agricultural production, distribution and consumption, and human waste treatment. These options include reducing fertilizer application rates to better match plant needs, reducing erosion rates, reducing food waste, and recycling human urine, which is rich in phosphorus and nitrogen. The authors state that their list of solutions is not exhaustive, but rather is meant to stimulate others to think about the sustainability challenges of the human P cycle. Indeed, missing in this paper’s list of solutions is a discussion of the role of fungi, which can access otherwise inaccessible soil phosphorus through symbiosis with plants.
Childers, Daniel L., et al., 2011, Sustainability challenges of phosphorus and food: solutions from closing the human phosphorus cycle, BioScience 61: 117–124, https://academic.oup.com/bioscience/article/61/2/117/242667