title: Fertilization strategies affect phosphorus forms and release from soils and suspended solids.
abstract: The release of phosphorus from soils in surface runoff is strongly influenced by fertilizer inputs and contributes significantly to agriculturally driven eutrophication. This work evaluated the forms and availability of P in bulk soils and suspended solids (SS) produced by a water dispersion test that mimics the action of rain events and/or irrigation. This test was applied on soils cultivated with maize and fertilized with mineral N, P, and K (NPK); mineral P and K (PK); bovine slurry and P (S); or manure and P (M) for 15 yr. The P surplus in the treated soils was in the order NPK < PK < S < M. Forms and availability of P were analyzed in bulk soils, and their respective SS (<20 μm) by the Hedley sequential P fractionation method and the isotopic exchange kinetics. The labile forms increased according to P surplus and represented up to 15 and 25% of total P in the bulk soil and in the SS, respectively, indicating a selective enrichment of the more labile P forms in the erodible particles. Exchangeability of P from SS was rapid and intense as a result of a shift of P solution equilibrium at the increased water/solid ratio and a larger accumulation of more labile P in the detached particles than in the bulk soil. Phosphorus saturation of iron and aluminum oxides and the enrichment of fertilizer-derived P salts in the suspended solids control P forms and exchangeability for mineral fertilizer treatments, whereas in M soil carbon content assumed a key role.
authors.forename: Teresa
authors.initials: T
authors.lastname: Borda
authors.forename: Luisella
authors.initials: L
authors.lastname: Celi
authors.forename: Else K
authors.initials: EK
authors.lastname: Bünemann
authors.forename: Astrid
authors.initials: A
authors.lastname: Oberson
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Frossard
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Barberis