Whether fresh from animals (including humans) or in fossilised form from birds and bats (called guano) manure is one source of Nature’s wonder macronutrient phosphorus.

Phosphorous is an essential nutrient for plant growth because it helps transform solar energy into the chemical energy that enables the plant’s growth by creating oils, sugars and starches.

It is also forms a part of the structure of human DNA and is an important element in our bones and teeth.Without it, no plant on earth could survive.

Outside of manure, phosphorous can be delivered back into the soil through ash and smoke, an approach used by Indigenous Australians who used –fire-stick farming’ to regularly burn vegetation.

Unfortunately, these methods of recycling phosphorus have been interrupted by our modern lifestyles.

As Earth’s population has increased, so too has the global demand for food, causing rapid depletion of natural phosphorus in soils through intensive agriculture.

An ongoing cycle that removes phosphorus from the soil in one location through farming, to be consumed by humans or animals as food thousands of kilometres away, then transported to sewage or landfill means our natural phosphorus is being removed from its original location and never replaced.

This cycle, combined with increased demand for food means fertilizers have become an essential part of modern farming. The mining of phosphate rock and the subsequent manufacture of phosphate rich fertilizers provides the boost of phosphorus needed to help increase food production [i].

But phosphate rock is a finite resource. It takes 10-15 million years to form and much like oil is non-renewable. Scientists are not sure how much viable phosphate rock is left in the world, but demand is expected to climb as the world’s population increases[ii].

To preserve our phosphorus resources, we must find ways of using less phosphorus in the first place, as well as increasing the recycling of phosphorus back into the soil.

Farmers and scientists are already working on ways to use phosphorus resources more efficiently.

This ranges from relatively simple measures like returning unused crop parts (such as inedible roots or stalks) back into the soil, to the more technologically intensive like finding ways to make the phosphorus in soil easier for plants to absorb [iii] and investigating ways to recover struvite (phosphorus rich ammonium magnesium phosphate crystals) from wastewater.

Countries such as Sweden are trialling urine diverting toilets which can return phosphorus rich urine to agricultural areas without contamination from other waste [i]. In Australia, Sydney Water also has a program to produce fertilizers from sewage.

Action is also possible on an individual level.

Reducing waste and composting food scraps instead of throwing them away means any unused phosphorus is returned to the soil.

This is even more effective if the fruit and vegetables were grown in the back yard in the first place. Also using natural fertilizers like manure, instead of the artificial variety helps to maintain the natural phosphorus cycle.

[i] Cordell D, Drangert J-O and White S, (2009) The story of phosphorus: Global food security and food for thought. Global Environmental Change: Volume 19, pp 292-305. http://www.agci.org/dB/PDFs/09S2_TCrews_StoryofP.pdf

[ii] Cordell D, White S, (2010) The Australian story of phosphorus: sustainability implications of global phosphate scarcity for a net food-producing nation. Academic manuscript. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-53767

[iii] Guppy CN, and McLaughlin MJ, (2009) Options for increasing the biological cycling of phosphorus in low-input and organic agricultural systems. Crop and Pasture Science: Volume 60, pp116-123. http://www.publish.csiro.au/issue/5243.htm