Identification and quantification of phosphate turnover indicators after long-term compost application – long-term and single season effects

Background and aims Soil organic phosphorus (P org ) is of interest for plant nutrition because it can comprise between 20 and 80% of total soil phosphate (P). This study aims to examine the effect of compost application on soil phosphatases and microbial biomass, which influence the P turnover and, furthermore, to examine the speciation of P org . Methods Soil from a long-term field experiment (since 1997) which compares compost application with inorganic fertilization was analyzed for calcium-acetate-lactate extractable P (CAL-P), Olsen-P, acid (Acid-P ase ) and alkaline (Alk-P ase ) phosphatase activity and microbial biomass P. P org speciation was additionally analyzed with liquid-state 31 P nuclear magnetic resonance spectroscopy ( 31 P-NMR). Results We found a significant increasing long-term effect of high compost application (equivalent to 400 kg ha −1 N (400)) on Acid-P ase (45%) and Alk-P ase (58%). After compost application, Acid-P ase increased by 41% in treatment 400 (3 days after compost application (DAA)). The 31 P-NMR analysis showed a significant increase of inorganic orthophosphate (55%) after high compost application. Furthermore, the total phosphomonoester region was significantly decreased in the treatment 400 (8%). Conclusions We demonstrated that long-term compost application increases phosphatase activity which plays a key role in the mineralization of soil P org . In particular, the decrease of the concentration of P org species in the phosphomonoester region in the treatment 400 with high compost application highlights that an increased turnover affects this soil P pool and may provide P to plants. This knowledge provides a better understanding of how the P cycle responds to long-term compost fertilization.