Status: this discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The manuscript was not accepted for further review after discussion.
Phosphorus and carbon in soil particle size fractions – A global synthesis
Marie Spohn
Abstract. Despite the importance of phosphorus (P) as a macronutrient, the factors controlling storage of organic phosphorus (OP) in soils are not yet well understood. The objective of this meta-analysis was therefore to investigate the distribution of OP, organic carbon (OC), and inorganic P (IP) in particle size fractions depending on climate, latitude and land use, based on data from published studies. The clay size fraction contained on average 8.8 times more OP than the sand size fraction and 3.9 and 3.2 times more IP and OC, respectively. The OP concentrations of the silt size and clay size fractions were both most strongly correlated with mean annual temperature (MAT) (R2 = 0.30 and 0.31, respectively, p < 0.001). Latitude, MAT and mean annual precipitation together largely explained the variability of the OC concentration of the clay size fraction (R2 = 0.73, p < 0.001). The OC : OP ratios of the silt and clay size fraction were correlated with latitude (R2 = 0.49 and 0.34, respectively, p < 0.001), and the OC : OP ratio of the clay size fraction changed less strongly with latitude than the OC : OP ratio of the silt and the sand size fraction. The OC concentrations of all particle size fractions were significantly (p < 0.05) lower in the croplands than in the adjacent soils under (semi-)natural vegetation. In contrast, the OP concentration was only significantly (p < 0.05) decreased in the sand size fraction due to land use conversion. In conclusion, this meta-analysis shows that OP concentrations in the silt and clay size fraction strongly depend on climate and latitude, and that OP is more strongly enriched in the clay size fraction than OC and IP, which is likely due to the fact that OP competes very successfully for sorption sites in soil. The strong sorption of OP in soil, especially in the clay size fraction, makes OP less vulnerable to land-use change than soil OC.
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Phosphorus (P) supply for agriculture will likely decrease in the future. Therefore, it is important to understand the behavior of phosphorus in soils. The study shows that soil organic phosphorus concentrations depend on climate, and that organic P is more strongly enriched in the clay size fraction than organic carbon (C) and inorganic P. The strong sorption of organic P in soil, especially in the clay size fraction, makes organic P less vulnerable to land-use change than soil organic C.
Phosphorus (P) supply for agriculture will likely decrease in the future. Therefore, it is...
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