(FAO 2010) estimated the world’s population to consist out of 9.1 billion people in 2050 (growth of 34%), to feed all these people the food production has to increase 70%. The food production has to increase that much, not only due to population growth, but also due to the urbanization and welfare growth resulting in more diverse diets (FAO 2010). Besides there is the uncertain need of agricultural biomass for bio-fuel production, and the degradation of the natural resources (FAO 2010). So it is getting hard to produce enough food to feed the world population in the future, but according to (FAO 2010) it is possible to meet the food demands of the future by making adequate use of the natural resources.
One of these important resources is phosphorus, especially because it is non-renewable (Manske, Ortiz-Monasterio et al. 2000). ‘Nutrients are namely often the most limiting factor for crop growth’ (Duivenbooden, Wit et al. 1995) and rock phosphate, the source of P-fertilizer, is probably depleted over 60-90 years (Juroszek, Lumpkin et al. 2008). Furthermore 80% of the phosphorus is lost in processes between the mining and feeding of people (GPRI 2010). So to sustain the food security in the future, the available P-fertilizers have to be used more efficient (Duivenbooden, Wit et al. 1995) and phosphorus has to be recovered as much as possible from “waste” products (GPRI 2010).
The plant-available P-content in the soil is mainly controlled by the concentrate of phosphate ions in the soil solution and the P-buffer capacity of the soil (Syers, Johnston et al. 2008). The P is mainly buffered by OM, Al and Fe oxides (Blake, Mercik et al. 2000), both organic and inorganic P (Wolf, De Wit et al. 1987). Through this P-buffer capacity, the inorganic P is moved to the root surface mainly by diffusion and to lesser extent via mass flow (Syers, Johnston et al. 2008). By this the P-buffer capacity, provided sufficient adsorbed P, can deliver enough P to supply the crop P-demand (Syers, Johnston et al. 2008).
Plants do take up P mainly in the form of H2PO4-1 and to lesser extent in the form of HPO4-2(Syers, Johnston et al. 2008). The minimum concentration at which plants can take up P from the soil solution is 1µM (Hendriks, Claassen et al. 2007). Important factor for enough P-uptake is an extensive root system, with a lot of root hairs and symbiosis with mycorrhizal fungi (is specific per plant species) (Syers, Johnston et al. 2008). In P-deficient soils, 90% of the P can be taken up by the root hairs (Syers, Johnston et al. 2008). So the root system characteristics are important factors which determine to what extent the plant can take up P from the soil solution.
Only a (small) fraction of the applied P-fertilizer is taken up by plants, the so called apparent recovery fraction (Duivenbooden, Wit et al. 1995). This is affected by different processes, e.g. the earlier mentioned P buffering by OM, Al and Fe oxides, but also due to irreversible P binding to soil particles or leaching (Duivenbooden, Wit et al. 1995). Resulting, mainly in the developing world, into P-deficient growing conditions (Manske, Ortiz-Monasterio et al. 2000).
According to FAOSTAT wheat, maize and rice were the three most produced food crops in 2004. Wheat e.g. is for about 1.5 billion people the main source of calories (Manske, Ortiz-Monasterio et al. 2001), which have a low apparent P-recovery fraction of about 10 to 30% (Manske, Ortiz-Monasterio et al. 2000). To be able to model the future food security in relation to the declining P-availability, the P-recovery fraction per soil type is needed. The objective of this report was to investigate the P-recovery fraction per soil type for wheat. So in this report has been looked, via literature study, to P-fertilizer recovery fractions for wheat grown on different soil-types, which at the end have resulted in a short overview of all the found P-recovery fractions.