Phosphorus stocks and speciation in a soil profile of a long-term fertilization experiment: evidence from sequential fractionation, P K-edge XANES, and 31P-NMR spectroscopy

Up to 80% of the P applied by inorganic (triple super phosphate =TSP) or organic (manure or compost) fertilizer P is not directly taken up by plants and, thus, can accumulate in the topsoil or subsoil. However, only rare information is available on the speciation, bioavailability, and overall the amount of P stored in the subsoil and how this is affected by different fertilization practices. Filling this knowledge gap can help to increase the utilization of this still underrated P source in the subsoil and thus over the long term reduce the chemical fertilizer application levels. Therefore, the objective of our research was to quantify the P stocks, P speciation, and availability in the soil profile as function of four different P fertilization treatments