Phosphorus fertility assessment of intensively farmed areas of catchments draining to the Great Barrier Reef World Heritage Area; 2: Potential of soils to release soluble phosphorus

The potential of fertilized cropping soils ( sugarcane, vegetables, fruit trees) in river catchments that drain to the Great Barrier Reef World Heritage Area in northeastern Australia to release soluble phosphorus ( P) was assessed using soil chemical tests on typical soils (0-10 cm) collected in 2003. Tests included total P, diagnostic soil P tests, estimates of P buffering, and soluble and redox sensitive soil P. Routine soil P tests proved poor predictors of CaCl2 P (0.005 M). Values >= 0.20 for the Mehlich-3 P saturation ratio separated (P < 0.01) lower from higher concentrations of CaCl2 P. The ratio of Mehlich-3 Fe to [Mehlich-3 Fe + Mehlich-3 Al] is offered as a possible simple index of redox sensitive P. Part 1 (Rayment and Bloesch 2006) describes the soil survey in more detail.