Incubation of Dried and Sieved Soils Can Induce Calcium Phosphate Precipitation/Adsorption

Soil incubations are a common practice typically employed in assessing the effect of some treatment on the availability and solubility of phosphorus (P). However, standard sample preparation (drying and sieving) can alter soil chemical and physical properties, resulting in possible changes in P behavior upon soil incubation. Sixty surface soil samples were collected, air dried, and sieved before being incubated at field capacity for 7 days. After incubation, soils were allowed to air dry and were analyzed along with nonincubated samples for pH and waterand Mehlich3-extractable elements. Incubation increased pH and decreased water-soluble P, calcium (Ca), and magnesium (Mg) relative to nonincubated soils. Increases in pH may have been due to increased solubility of residual calcium carbonates by drying and sieving. This increase in pH among soils with sufficient levels of P, Ca, and Mg resulted in the formation of Ca and Mg phosphates as confirmed by chemical speciation modeling.