Addition of phosphorus to soils with low to medium phosphorus retention capacities. II. Effect on soil phosphorus extractability

Knowledge of the change in soil extractable phosphorus (P) as a consequence of soil P fertilization could be useful in discriminating soils with a potential for soil P release to runoff or movement of P along the soil profile. In this research, soils with low to medium P retention capacity were equilibrated for 90 days with soluble P (KH,PO,) at rate of 100 mg P kg(-1) soil. After this period, soil samples both with and without the P addition were analyzed using six conventional methods: 1)Olsen, 2) Brayl, 3) Mehlich3, 4) Egner, 5) Houba, dilute CaCl2 solution, and 6) distilled water, and three "innovative" P-sink methodologies: 1) Fe oxide-coated paper strip, 2) anion exchange resin membrane, and 3) cation-anion exchange resin membrane. The soils without P addition had low levels of extracted P as determined by all nine procedures. Net increases in the amount of P extracted from the soils with added P ranged from 4.2 mg kg(-1) (CaCl2 extraction) to 57.6 mg kg(-1) (cation-anion resin membrane extraction). Relationships between change in extracted P and i) physical and chemical characteristics, and ii) soil P sorption properties are also presented and discussed.