Phosphorus sorption maxima and desorbability in selected soils with andic properties from the Azores, Portugal

Abstract

P sorption and desorption capacities were determined on 30 soil horizons (surface and subsurface) of soils with andic properties from the Azores, Portugal, using the Langmuir equation and successive extractions with dilute calcium chloride (CaCl 2), respectively. The proportion of P recovery (P rec) using distilled water (H 2O), CaCl 2, Bray 2 (B2), Mehlich 3 (M3), Egnér–Riehm (ER) and Olsen (OL) extractants was also determined to assess the extent of P release from soils enriched with P at P sorption maxima (P m). Soils containing very low amounts of organic C and allophane (Vitrandic Haplustepts and Vitrandic Udorthents) showed the lowest values of P m (48–565 mg kg − 1 ) and the highest values of P desorbability (P des) (69–100%), indicating that P can be easily lost from these soils. Application of fertilizers to these soils should be restrained in order to minimize eutrophication risk of nearby water bodies. In contrast, allophanic and non-allophanic horizons of Typic Placudands, Alic Hapludands, Acrudoxic Hapludands and Acrudoxic Hydrudands showed much higher values of P m (2273–52,400 mg kg − 1 ) and lower values of P des (4–57%).They also showed low proportions of P rec by the used extractants, indicating that large amounts of P can be sorbed in an unavailable form. Thus, these soils may require large amounts of P fertilizers and an efficient method of P application. Other studied soils with high amounts of 1:1 layer silicate minerals and having weak andic properties (Typic and Andic Haplustepts), showed intermediate P m (1124–8333 mg kg − 1 ) and P des values (20–63%). The values of P m were positively correlated with Al d, Al o, allophane, Fe o, Fe d and Al p contents, and with the values of Al o + 1/2 Fe o. In contrast, values of P des were negatively correlated with these soil constituents. Of the six extractants, the B2 extractant showed generally higher proportions of P rec than the other extractants in most studied soils. The proportions of P rec by the B2, M3, ER and OL extractants were negatively correlated with contents of Fe o, Fe d, Al d, Al o, Al p, and Fe p, and with the values of Al o + 1/2 Fe o and PR.