Why do we need phosphorus
How can it help to keep the world fed
In the worst-case scenario, available supplies of phosphorus on Earth will run out in 50 years. It won’t disappear completely, of course, but we will no longer be able to mine it in the same way.
Why do we need phosphorus for anyway?
Phosphorus is present in DNA, so without it life on Earth (in the forms we know) is impossible. Additionally, it is part of ATP – adenosine triphosphate – a compound which contains two high-energy bonds, and serves as an energy source for many energy-intensive biochemical and physiological processes in the body. Additionally, phosphorus assists the growth and recovery of the body.
In agriculture, phosphorus is used widely in fertilizers and fodder additives. So, we depend on phosphorus to keep the world fed.
In the first half of the 19th century, the Swiss historian and political scientist Justus von Liebig popularized the Law of the Minimum for agriculture. According to this law, growth is limited by the scarcest resource. The hydrogen, oxygen and carbon that plants require are easily obtained from water and carbon dioxide. From the moment that people learned to synthesize ammonia, there has also been enough nitrogen. So phosphorus became the limiting factor in agriculture.
The lion’s share of the world production of phosphorus comes from the Western Sahara – a former Spanish colony which now belongs to Morocco. These mines contain 70% of available phosphorus. At the same time, scientists warn that the time is approaching when production will not be able to keep up with people’s requirements.
How did this happen?
In nature, phosphorus is only encountered in a bond with oxygen, which forms phosphate. In this form, it is also mined. Chemists can separate the oxygen and obtain pure white phosphorus, which glows in the dark. But it is so unstable that it immediately catches fire as soon as it comes into contact with air. Phosphate easily enters the soil and water and is absorbed by living cells. If it comes into contact with calcium or iron, it creates highly insoluble salts.
In the past, the fertilizer used in farming was made of bones dug up in old battlefields, approximately half of which consisted of hydroxyapatite, a mineral containing phosphorus – Ca₁₀(PO₄)₆(OH)₂. Guano (large heaps of bird dung) also contains a lot of phosphorus, and was also used in agriculture. But these resources soon ran out, and people’s growing needs required new methods to obtain phosphorus. It began to be mined.
But there are also problems with these methods. Phosphates are easily washed out of soil by ground waters, and phosphates from mines end up in the ocean. They settle on the ocean floor in the form of calcium phosphates, or are absorbed by sea creatures, and after the creatures die these phosphates also settle on the ocean floor. In any case, they become inaccessible for us.
Inevitable losses
Everything is complicated by the fact that only 1 in every 5 kilograms of phosphorus is absorbed by the plants which we try to fertilize. It is partially washed away by ground waters, and partially bonds with calcium and iron in the soil. And although the roots of some plants are capable of extracting phosphorus from these bonds, they cannot extract all of it. Additionally, agricultural lands are deprived of phosphorus during harvest time.
In the soil of virgin ecosystems – forests and wild grasslands – the majority of phosphorus is present in the form of organic compounds. Inorganic phosphates absorbed by animals, plants and microorganisms are retained in cells in the form of organic substances: phospholipids, phytate and other compounds containing phosphorus, and after the death of the organism, they return to the soil. This finely-tuned system formed over millions of years. And its stability depends on the number and activity of organisms participating in the process. In agriculture, in order to maintain an abundance of microbes in the soil that are capable of retaining phosphorus, fields are fertilized with manure.
But livestock breeding – the only source for the required quantity of manure – requires an enormous amount of phosphorus itself. Phosphorus compounds take part in all the processes involving the animals’ growth. So the animals’ ration is artificially enriched with it. It’s a vicious cycle of phosphorus deficit!
People also waste a lot of phosphorus. Most of it, even when it is present in our food, is flushed down the drain. There are technologies for extracting it from waste water, but they are currently too expensive to be used in practice.
We constantly scatter phosphorus around us, and it settles on the ocean floor, although this is not our fault. At the same time, we should pay more attention to microorganisms living in soil, and the role that they play in preserving phosphorus. Otherwise our world will no longer be able to feed itself at an acceptable cost.
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