Phosphorus Transformations and Their Relationships with Calcareous Soil Properties of Southern Western Australia

Abstract

The agronomic effectiveness of phosphate fertilizers is strongly affected by reactions of P with soil constituents. The transformation of P added to soil and the effect of soil properties on these transformations was investigated for 14 alkaline and calcareous soils from southern Western Australia. The decline of NaHCO3‐extractable P (Olsen‐P) with time followed a second order kinetic equation. The kinetic rate constant (k) increased with increasing oxalate‐extractable Fe (Feo), citrate–dithionite–bicarbonate (CDB)‐extractable Al and Fe (Ald and Fed), CaCO3‐free clay content, cation‐exchange capacity (CEC), and ratio of CDB‐extractable Fe (Fed) to active CaCO3 equivalent (ACCE), and k decreased with increasing ACCE. A combination of these soil properties described 93% of the variation in rate constant, of which 78% of the variation was predicted by the Fed/ACCE ratio alone. A combination of clay related properties (Ald, clay, Feo, and CEC) described 62% of the variation in Ca2–P determined by specific extraction. Carbonate‐related properties (ACCE and CCE) together described 71% variation in Ca8–P. Clay‐related and carbonate‐related properties jointly described 97% and 81% of the variation in Fe–P and Olsen‐P respectively. Surface area (SA) and Ald together accounted for 43% of the variation in Al–P. Scanning electron microscopy analyses showed that added P was uniformly distributed in the soil matrix to the limit of the spatial resolution of the technique (≈2 μm).