Isolation and characterization of labile organic phosphorus pools in soils from the Askov long-term field experiments

Summary

Labile soil organic phosphorus (Po) plays a crucial role in plant P nutrition and in environmental eutrophication. This paper discusses recent studies on the nature of labile soil Po and its response to different fertilization practices. Soil material was obtained from the Askov long-term experiment on animal manure and mineral fertilizers. Our analytical approach combined a macroporous anion exchange resin to isolate labile Po and 31P NMR spectroscopy to assess the chemical composition and origin of NaOH-extractable Po. The analyses were carried out on fine earth (<2 mm) and particle-size fractions. The results suggest that the resin extraction isolates an active pool of soil Po that consists primarily of microbially-derived compounds. The size of the active Po pool reflects seasonal variations and P fertilization. However, the source of added P (NPK vs. animal manure) appears to have only little influence on the labile Po. Our results further suggest that most of the active soil Po is associated with clay sized separates (<2 μm), indicating this fraction being important in the short-term turnover of Po.