Effect of soils with varying degree of weathering and pH values on phosphorus sorption

• Oxides affect P sorption over CaCO3 in soils differing in weathering.
• CaCO3 and pH become predominant in P sorption in same-weathering soils.
• P sorption was higher in Alfisols compared to Entisols and Inceptisols.

Various soil properties are known to influence P retention, but it is not clear which of them are predominant when soils of different degree of weathering are compared, and which when newly developed soils differ mainly in activity (pH). We chose 23 typical Mediterranean low organic matter-content soils: 13 of them differed in weathering (4 Alfisols, 4 Entisols, and 5 Inceptisols), and 10 were newly developed Entisols, of which 5 were acidic and 5 alkaline. We conducted batch P sorption tests at C0 = 0–100 mg L− 1, measured important soil physico-chemical properties, and correlated them with sorption indices. Alfisols were significantly higher in total “free” Al and Fe, as well as in well-crystalline oxides, and this led to higher P sorption by Alfisols. Correlation analyses in the activity-divided soils revealed that amorphous oxides, although significantly higher in the acidic soils compared to the calcaric, did not have any influence in P sorption, neither did any other oxides species, while CaCO3, along with pH, were the important factors to enhanced P retention. Contrary to that, in the taxonomy-divided soils, neither pH nor CaCO3 played any significant role in P sorption, which was rather influenced by oxides (mainly the amorphous, but to a lesser degree by the crystalline species as well). We conclude that oxides are the key soil property influencing P sorption among soils of different weathering (even if these soils also differ in pH and CaCO3), while within the same taxonomic order, CaCO3 and pH becomes the important factor.