The story of phosphorus: Global food security and food for thought
Introduction
Food production is fundamental to our existence, yet we are using up the world's supply of phosphorus, a critical ingredient in growing food. Today, phosphorus is mostly obtained from mined rock phosphate and is often combined in mineral fertilizers with sulphuric acid, nitrogen, and potassium. Existing rock phosphate reserves could be exhausted in the next 50–100 years (Steen, 1998, Smil, 2000b, Gunther, 2005). The fertilizer industry recognises that the quality of reserves is declining and the cost of extraction, processing and shipping is increasing (Runge-Metzger, 1995, Driver, 1998, Smil, 2000b, EcoSanRes, 2003). Box 1 outlines the key issues.
Common responses to resource scarcity problems include higher prices, more efficient resource use, the introduction of alternatives, and the recovery of the resource after use. The use of phosphorus is becoming more efficient, especially in Europe. Farmers in Europe and North America are increasingly avoiding over fertilization, and are ploughing straw and animal manure into agricultural soils, partly to recycle phosphorus (European Fertilizer Manufacturers Association, 2000). However, most of the discussion about efficient phosphorus use, and most of the measures to achieve this, have been motivated by concerns about toxic algal blooms caused by the leakage of phosphorus (and nitrogen) from agricultural land (Sharpley et al., 2005). While such measures are essential, they will not by themselves be sufficient to achieve phosphorus sustainability. A more integrated and effective approach to the management of the phosphorus cycle is needed—an approach which addresses future phosphorus scarcity and hence explores synergies that reduce leakage and recover and reuse phosphorus.
The following sections of this paper assess the historical, current and future availability of phosphorus in the context of global food security. Possible options for meeting the world's future phosphorus demand are outlined and institutional opportunities and obstacles are discussed.
Section snippets
Humanity's addiction to phosphate rock
Historically, crop production relied on natural levels of soil phosphorus and the addition of locally available organic matter like manure and human excreta (Mårald, 1998). To keep up with increased food demand due to rapid population growth in the 20th century, guano and later rock phosphate were applied extensively to food crops (Brink, 1977, Smil, 2000b). Fig. 1 gives a broad outline of the evolution of phosphorus fertilizer use for food production.
The Chinese used human excreta (‘night
Demand for food, demand for fertilizers
Following more than half a century of generous application of inorganic high-grade phosphorus and nitrogen fertilizers, agricultural soils in Europe and North America are now said to have surpassed ‘critical’ phosphorus levels, and thus only require light applications to replace what is lost in harvest (FAO, 2006; European Fertilizer Manufacturers Association, 2000). Consequently, demand for phosphorus in these regions has stabilized or is decreasing.
However in developing and emerging economies
Peak phosphorus—a sequel to peak oil?
As first highlighted by Hubbert in 1949 (Hubbert, 1949), production of oil reserves will at some time reach a maximum rate or ‘peak’ based on the finite nature of non-renewable resources, after which point production will decline. In a similar way, the rate of global production of high-grade phosphate rock will eventually reach a maximum or peak. Hubbert and later others argue that the important period is not when 100% of the reserve is depleted, but rather when the high quality, highly
Options for sustainable phosphorus use and management
There is no single ‘quick fix’ solution to current dependence on phosphate rock for phosphorus fertilizers. However there are a number of technologies and policy options that exist today at various stages of development – from research to demonstration and implementation – that together could meet future phosphate fertilizer needs for global food production. Implementing these measures will inevitably require an integrated approach that looks beyond the current focus on reducing agricultural
Institutional and attitudinal barriers and opportunities
Since a global phosphorus scarcity crisis is imminent, as we have demonstrated in the sections above, why is it not being discussed in relation to global food security or global environmental change? What are the current barriers to addressing a phosphorus ‘crisis’ and what are the underlying reasons for the lack of attention to nutrient recirculation options such as urine reuse?12
Conclusions
This paper outlines how humanity became addicted to phosphate rock, and examines the current and future implications of this dependence on a non-renewable resource. Global demand for crops will continue to rise over the next half century, increasing the demand for phosphate fertilizers. However, modern agriculture is currently relying on a non-renewable resource and future phosphate rock is likely to yield lower quality phosphorus at a higher price. If significant physical and institutional
Acknowledgements
This research has been undertaken as a doctoral research project funded by an Australian Postgraduate Award (APA) issued by the Australian Department of Education, Science and Training (www.dest.gov.au).
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