1. Introduction 7 Phosphorus occurs naturally in the form of different phosphate minerals, hence phosphorus is commonly expressed – and referred to – as phosphate (see Text Box 1). Phosphorus plays a key role in the major photosynthetic and metabolic pathways and is an essential nutrient for all the earth’s living organisms. The rapidly increasing human population in the world and the concomitant increase in prosperity in some parts of the world have greatly increased the demand for crop- and animal-derived food during the last few decades (Ma et al, 2010). Modern agriculture relies heavily on phosphate addition to animal feed and the application of phosphate fertilisers for crop production, which makes phosphorus an essential constituent of the global food market. Moreover, the production of biomass for biofuels also relies on phosphate application, and thereby also tends to increase the global demand for phosphate. Phosphate should be regarded as an indispensable resource for plants, animals and people. Although the current geological phosphate resources are still sufficient to meet the growing demand of the near future, phosphate resources are – as with oil resources - finite. Because large phosphate reserves are found in only a few countries - including Morocco, China, South Africa and the USA phosphate should also be regarded as a strategic, geo-political commodity. After a long period of relative stability, phosphate prices have become unstable: Prices increased from 2007 onwards, peaked in 2008 followed by a decline to the price level of 2007 and are currently (June 2010) again increasing (USGS, 2009). The reason for this sharp price increase is not immediately clear, but growing demand for fertiliser for production of crop- and animal-derived food, biofuels as well as a Pagina 16

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