SOIL PHOSPHORUS DYNAMICS AFTER TEN ANNUAL APPLICATIONS OF MINERAL FERTILIZERS AND LIQUID DAIRY MANURE FRACTIONATION AND PATH ANALYSES

Knowledge of phosphorus (P) dynamics in soil is essential for predicting its bioavailability and the risk of P transfer from soil to bodies of water. A comparative study was conducted to assess the changes in P fractions and pathways of P transformation in soil measured after 10 annual applications of mineral fertilizers (MIN) and liquid dairy manure (LDM). Fractionation and path analyses were performed to quantify inorganic P (Pi) and organic P (Po) forms and the relationships between P pools in the 0 to 15-cm layer of a Labarre silty clay (fine, mixed, frigid, Humic Cryaquept) under barley monoculture. The MIN additions resulted in larger increases in Pifractions and smaller increases in the NaOH-Pocompared with the LDM applications. The LDM, however, produced 1.9 times more total soil labile P than the MIN plot. Path analysis indicated that path coefficients between the source and recipient P pools were P-source dependent. The NaOH-Piwas a primary sink of added Piand a source of NaHCO3-Pi. The roles of Popools were more important than the Pipools for P transformations. The NaHCO3-Powas sensitive to P sources and likely acted as a transitory pool rather than as a sink or source of soil P. The NaOH-Poconstituted a sink for added Poand immobilized labile Piin the MIN plot; it was conversely mineralized and contributed to labile Piin the LDM plot. The results of this study stress that the pathways of P transformation in this Cryaquept can be revealed by the descriptive path analysis.