Kinetics of inorganic and organic P release from red clover (Trifolium pratense L.) and ryegrass (Lolium multiflorum L.) upon frost or drying

Abstract

ABSTRACTAn incubation study with fresh, frozen, and dried clover and rye-grass shoots gathered in autumn was performed in the laboratory (43 days). The aim was to study inorganic and organic phosphorus (P) release from plant material during decomposition without soil. Plant materials (2 cm size) were mixed with small glass beads and placed in large syringes for consecutive water extractions on 7 occasions. Leachates were analysed for inorganic and total P. At the first leaching event, 8% of total crop P was released from fresh, 24% from frozen and 27% from dried plant material. During decomposition, both inorganic and organic P was released following first order kinetics, with grass releasing mostly inorganic P and clover mostly organic P. After 43 days, 42%–50% of total crop P from fresh, 49%–51% from frozen and 57%–69% from dried material was released, with significant differences between treatments. Using the results in calculations on field scale showed that P released from overwintering crops under cold climate conditions can amount to several kg P ha−1. Thus, senescence of overwintering aboveground biomass can be a significant source for P leaching from soils.