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

Abstract

Abstract Background and aims Soil organic phosphorus (Porg) 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 Porg. 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-Pase) and alkaline (Alk-Pase) phosphatase activity and microbial biomass P. Porg speciation was additionally analyzed with liquid-state 31P nuclear magnetic resonance spectroscopy (31P-NMR). Results We found a significant increasing long-term effect of high compost application (equivalent to 400 kg ha−1 N (400)) on Acid-Pase (45%) and Alk-Pase (58%). After compost application, Acid-Pase increased by 41% in treatment 400 (3 days after compost application (DAA)). The 31P-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 Porg. In particular, the decrease of the concentration of Porg 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.