Fig. 4. Saturation indices (SI) of P minerals in the equilibrated adsorption solutions of preincubated, reduced, and reoxidized(A) cultivated degraded peat (CDP), (B) fallow degraded peat (FDP), (C) nondegraded noncalcareous peat (NDNCP), and (D) marl soils. The SI values for the P minerals were calculated according to the thermodynamic stability constants of Lindsay (1979): brushite, CaHPO4·2H2O; octacalcium phosphate, Ca4H(PO4)3·2.5H2O; beta-calcium phosphate, ß-Ca3(PO4)2; hydroxyapatite, Ca5(PO4)3OH; MnHPO4; strengite, FePO4·2H2O; and vivianite, Fe3(PO4)2·8H2O. Data for the oxidized soils were taken from adsorption experiments conducted under aerobic conditions and data for the reduced soils were taken from experiments conducted under N2 atmosphere.