The solubility and mobility of soil phosphorus were determined up 60 cm depth from 1991 to 2002 in an experimental site continuously cropped by rye-grass. The experiment included an untreated plot and four plots which were spread by the same important amounts of pig slurry (4900 m3 ha-1) from March 1991 to October 1995. Soils were sampled in all plots in 1991, 1992, 1993, 1994, 1995, 1996, 1999 and 2002. The phosphorus solubility were determined in soil suspensions (1g:10ml) after filtration (0.2 µm) by the molybdate reactive phosphorus concentration (Cp, mg P/ L-1). In the same soil suspensions, the phosphorus mobility were determined by determining the gross amount of phosphate ions transferred between soil and solution using an isotopic labelling and dilution procedure. Since the experiment was isolated by a polymer film, the amount of P leached at 80 cm depth was determined every year multiplying the volume of drained waters (in average 331 mm per year) by their total phosphorus concentration. The phosphorus applied as pig slurry amounted 7964 kg P ha-1. The Cp value in the 0-20 cm layer of soil drastically increased from 0.06 (in 1991) to 12.0 mg P L-1 in 1996 before decreasing slightly up to 2002 as soon as the spreading of manures were stopped. Also, the Cp value in the 20-40 cm and the 40-60 cm layers of soil highly and continuously increased up to 2002 without reaching an equilibrium value. The dynamic of the mobility of soil phosphorus (Pr, mg P kg-1) in all samples depended both of time (t, minute) and Cp and closely fitted to the following function: Pr=28,1Cp0,41 t0,28, 24 obs. (r²=0,99). After 12 years of experimentation, the annual P leached at 80 cm depth is low (about 0,1 kg P ha-1) without showing any trend. The phosphorus spread as pig slurry did not yet reach the 80 cm depth. However, the migration is effective but the high reactivity of the soil delayed the loss of phosphorus in drainage waters which should finally occurred soon and for a long time.