In a new commentary (subscription required) in Nature Geoscience, IIASA researchers Michael Obersteiner, Marijn van der Velde, and colleagues write about the problems facing the world’s food supply as we exhaust our supplies of phosphorus. Projections show that phosphorus supplies could run out in the next 40 to 400 years. In this interview, Obersteiner and van der Velde give more background on the “phosphorus trilemma.”
Why is phosphorus so important?
MV: Phosphorus is essential for life on Earth. It is a key component of DNA and cell membranes, and vital for cellular energy processes. Crops need phosphorus to grow. And to maintain crop production, and to make sure that soils remain productive, we have to add extra nitrogen and phosphorus as fertilizer. This is one of the food security issues in Africa where soils are suffering from nutrient depletion without replenishment.
Where do we get phosphorus and why is that supply in danger?
MO: Phosphorus is ubiquitous in the Earth’s crust. However, most of it is strongly bound in the soil , where plants cannot access it. Modern agriculture (which made human population explode) essentially began when we found ways to extract nitrogen from the air and phosphorus from minerals to make fertilizers for agricultural purposes.
The problem is that minable phosphorus is geographically concentrated in very few places. For example 75% of known reserves are located in Morocco and these reserves are limited. If, for example, political turmoil restricted access to the mines of Morocco, we would be in danger of short-term shortages that could lead to rising food prices or food insecurity in poor countries.
What problems do you expect as phosphorus becomes even more limited?
MO: The biggest problem we face is limited or no access to phosphorus fertilizers by the poor and food insecure.
MV: At the same time, rich countries apply excess fertilizers causing eutrophication to their lakes and rivers, while the poor cannot afford fertilizers.
What can be done about these problems?
MV: More efficient fertilizer application would make fertilizers cheaper to poor farmers, and at the same time help address the environmental problems. But in the long run we need to figure out how to produce food in a way that recycles nutrients at minimum loss rates. (This also includes losses from human excrement!)
To better solve the issues around long-term phosphorus availability and equitable use we also need better data on how much phosphate rock is remaining in the world and where it is located. Countries will need to be persuaded to collaborate on both these issues to ensure equity.
How does IIASA research inform this debate?
MV: In a paper we published earlier this year in PLOS ONE we showed the importance of soil phosphorus and the significant increases in yields that could be achieved in Africa with balanced micro-dosed applications of nitrogen and phosphorus. Available phosphorus in soils is generally low, especially in older weathered soils in the tropics where a lot of the phosphorus can be locked up in iron and aluminum complexes. We are currently investigating what application rates of nitrogen and phosphorus would be optimal for a range of soils and climates. This can then lead to better soil and nutrient management.
MO: In addition researchers in the Mitigation of Air Pollution and Greenhouse Gases program have been very active in finding solutions to the problem. For example: http://www.iiasa.ac.at/web/home/resources/multimedia/Podcasts/Our-Nutrient-World—Wilfried-Winiwarter-on-Reality-.en.html
What should people to know about this issue?
MO: Many things in nature that we like or depend on for our livelihood are substitutable. But phosphorus is in everything we eat and cannot be substituted by any element. If we continue business as usual we will squander this resource and thereby potentially compromising the wellbeing of our daughters and sons.
M. Obersteiner, J. Peñuelas, P. Ciais, M. van der Velde, and I.A. Janssens, 2013. The phosphorus trilemma. Nature Geoscience, 6, 897-898, doi:10.1038/ngeo1990 [COMMENTARY].
M. van der Velde, L. See, L. You, J. Balkovič, S. Fritz, N. Khabarov, M. Obersteiner and S. Wood, 2013.Affordable nutrient solutions for improved food security as evidenced by crop trials. PLoS ONE 8(4): e60075. doi:10.1371/journal.pone.0060075 [OPEN ACCESS].